Tuesday, September 30, 2008

Water that Stains

I have Red Stains in my Sinks and Other Fixtures -- Help!

Red stains are normally caused by iron in the water. You must test to determine the amount and the type of iron you have. Some types are: oxidized, soluble, colloidal, bacteria or organic-bound. All are a problem! It only takes 0.3 ppm to stain clothes, fixtures, etc.


This type of iron is usually found in a surface water supply. This is water that contains red particles when first drawn from the tap. The easiest way to remove this type of iron is by a fine mechanical filter. A cartridge type filter is usually not a good solution, due to the rapid plugging of the element. Another method or removal is by feeding a chemical into the water to cause the little particles of iron to clump together, and then fall to the bottom of a holding tank, where they can be flushed away.


Soluble iron is called "clear water" iron. After being drawn form the well and contacting the air, the iron oxidizes, or "rusts", forming reddish brown particles in the water. Depending on the amount of iron in the water, you may solve this problem with a water conditioner, or a combination of softener and filter. You may use an iron filter that recharges with chlorine or potassium permanganate, or feed chemicals to oxidize the iron and then filter it with a mechanical filter. You can sometimes hide the effects of soluble iron by adding chemicals that, in effect, coat the iron in the water and prevent it from reaching oxygen and oxidizing.

Colloidal iron is very small particles of oxidized iron suspended in the water. They are usually bound together with other substances. They resist agglomeration, i.e., the combining together of like substances forming larger, heavier, more filterable ones, due to the static electrical charge they carry. This iron looks more like a color than particles when held up in a clear glass, as they are so small. Treatment is usually one of two: Feed chlorine to oxidize the organic away from the iron, thus allowing agglomeration to occur, or, feeding polymers that attract the static charge on the particles, forming larger clumps of matter that is filterable.


Iron bacteria are living organisms that feed on the iron found in the water, pipes, fittings, etc. They build slime all along the water flow path. Occasionally, the slimy growths break free, causing extremely discolored water. If a large slug breaks loose, it can pass through to the point of use, plugging fixtures. These types of bacteria are becoming more common throughout the United States. If you suspect bacteria iron, look for a reddish or green slime buildup in your toilet flush tank. To confirm your suspicions, gather a sample of this slime and take it to your local health department, or water department for observation under the microscope. This type of iron problem is very hard to eliminate. You must kill the bacteria, usually by chlorination. You must use high amounts of chlorine throughout your plumbing system to kill all organisms. You may find it necessary to feed chlorine continuously to prevent re-growth. A filter alone will not solve this problem.

Organic bound

When iron combines with tannins and other organics, complexes are formed that cannot be removed by ion exchange or oxidizing filters. This iron may be mistaken for colloidal iron. Test for tannins; if they are present, it is most likely combined with the iron. Low level amounts of this pest can be removed by use of a carbon filter, which absorbs the complex. You must replace the carbon bed when it becomes saturated. Higher amounts require feeding chlorine to oxidize the organics to break apart from the iron and cause both to precipitate into a filterable particle.

I Have Blue or Green Stains on my Fixtures -- Help!

You either have copper in your water supply, or you have copper pipes and corrosive water. Test for copper in your water. Test the pH, total dissolved solids content and the oxygen content of your water.


Copper can be removed by ion exchange, i.e., a water softener. The removal rate is about the same as it is for iron.

Copper pipes and corrosive water

If your pH is from 5 to 7, you may raise it by passing the water through a sacrificial media. By sacrificing calcium carbonate into the water, the corrosively will be reduced. If the pH is below 5, you will need to feed chemicals into the water.

If the corrosively is caused by excess oxygen, the hot water will be much more corrosive than the cold. Treatment is by feeding polyphosphate or silicates to coat and protect the plumbing, or to aerate the water to release the excess oxygen.

Aquacheme : Water Treatment Specialist

Water Testing Information

When Should I test?
Several factors will influence when and how often you test your water. Where do get your water from? Has that source changed? Have you done any plumbing changes lately? Is there reason to believe that your water is contaminated? Is there a sickness or illness in your family affecting more than one person and over a longer than normal time period?

If you receive your water from a "Public Supply", i.e., a municipal supply, or a supply that provides water to more than 25 persons for 60 days per year (some states are different -- check with YOUR local water department), you can be fairly certain that the water supply is checked on a regular basis. The frequency of the testing is based on the number of people served, and may vary from more than once per week to once per month, or even less. Under these conditions, test when you move into a new residence to acquire a "base line" of contaminant level, if any. Retest every three years, unless you have reason to believe that something has changed that could affect the quality of your water.

If you have a private well, you are the only person who is responsible for the water your family drinks and bathes in. I recommend testing by your local Health Department every six months for Bacteria and Nitrate. These two tests serve as indicators for other types of contamination -- that is not to say forget the other tests; just that if you get a "bad" test from them, you should also retest for the other types of contaminants as well. Private wells should be tested on a regular basis for Pesticides, Herbicides, Metals, Organic and Inorganic chemicals and volatiles. Currently, no laws govern the frequency of such testing -- that is why I say YOU are the only person responsible for your family's water. I recommend an initial test (for a base line), and then at least once per year. Remember, one day after testing and finding "no contaminants", your source could become contaminated.

What Could I Test For?

Coliform bacteria are a group of microorganisms that are normally found in the intestinal tract of humans and other warm blooded animals, and in surface water. The presence of these organisms in drinking water suggest contamination from a surface or shallow subsurface source such as cesspool leakage, barnyard runoff or other source. The presence of these bacteria indicate that disease-causing (pathogenic) organisms may enter the drinking water supply in the same manner if preventive action is not taken. Drinking water should be free of Coliform.

Cysts and viruses are microbiological contaminants, usually found in surface water supplies. Giardia lamblia cysts can cause giardiasis, a gastrointestinal disease. Another "bug" getting a lot of attention lately, is cryptosporidium, single-cell parasite measuring about 2 - 5 microns in diameter. Many surface water supplies contain this pest, which also comes from the intestine of warm blooded animals.

Nitrate in drinking water supplies may reduce the oxygen carrying capacity of the blood (cyanosis) if ingested in sufficient amounts by infants under 6 months of age. This could cause a disease called "methemoglobinemia", or "blue baby" syndrome. The EPA has established a maximum contaminant level (MCL) for nitrate at 10 mg/l (ppm) measured as N. Unlike Coliform or other types of bacteria, boiling the water will actually INCREASE the amount of nitrate remaining in the water, increasing the danger to infants. If you have high nitrate water, either treat it with an approved treatment methodology or find another source: Boiling will only make it worse!

Lead is now known to leach from older sweat joints in copper pipe. As the water sits in the pipes, small amounts of lead 'dissolve' into the water, contaminating it. Lead is particularly harmful to small children as they more rapidly absorb the toxic substance into their systems. The EPA has estimated that more than 40 million U.S. residents use water that contains more than the recommended levels.

Health Effects of Selected Drinking Water Contaminants

Arsenic Malignant tumors of skin and lungs, cramps, spasms, effects to nervous system
Barium Prolonged stimulant action on muscles, nerve block
Benzene Associated with cancer, leukemia, anemia
Cadmium Bronchitis, anemia, gastrointestinal upsets, cancer in rats
Carbon tetrachloride Central nervous system depression, gastrointestinal effects, liver and kidney damage, coma, death
Chlordane* Carcinogen, liver and kidney damage
Chlorobenzene Irritation to respiratory system, central nervous system depression
Chloroform Possible liver, kidney and heart effects; carcinogenic in at least one animal species
Chromium Kidney damage, cancer
Copper Gastrointestinal tract irritant, possible infant fatality, Wilson's disease
Dichlorobenzene(s)* Suspected carcinogen
1,1-Dichloroethane Central nervous system depression, liver damage, suggested animal carcinogen
1,2-Dichloroethane Nausea, mental confusion, liver and kidney damage
Dichloroethylene* Nausea, dizziness
Ethylenedibromide (EDS) Decreased fertility
Fluoride Skeletal damage when present in high levels
Heptachlor Possible tumor induction, carcinogenic in test animals
Lead Damage to nervous system, kidneys, reproductive system; cancer in rats
Lindane Chronic liver damage, anemia, leukemia
Mercury Kidney impairment, possible death
Methylene chloride* Toxic
Nickel Signs of hyperglycemia and gastrointestinal and nervous disorders
Pentachlorophenol (PCP) Loss of appetite, respiratory difficulties, anesthesia, coma, death
PCBs Damage to skin and liver; nausea, loss of weight, jaundice, coma, death
Selenium Carcinogen; irritation to mucous membranes, dermatitis
Sulfate Laxative action
Tetrachloroethylene Central nervous system effects; confirmed animal carcinogen, anesthesia, death
Toluene Narcosis, irritation to eyes and respiratory system
Toxaphene Possible liver damage
1,1,1-Trichloroethane Narcosis, depression of central nervous system, unconsciousness, death
1,1,2-Trichloroethane Possible liver and kidney effects, possible carcinogen in animals
Trichloroethylene Central nervous system depression, loss of coordination, unconsciousness; strong irritant and carcinogen
2,4,6-Trichlorophenol* Suspected carcinogen
Trihalomethanes (THMs) Effects to nervous system and muscles, loss of consciousness
Vinyl chloride Central nervous system depression, dulling of visual and auditory responses, possible death
Xylene Mucous membrane irritant, lung congestion, impairment of kidney functions
Zinc Muscular stiffness and pain, loss of appetite, nausea

Hard Water

What is hard water?

Hard water is the most common problem found in the average home. Hard water is water that contains dissolved hardness minerals above 1 GPG.

What are hardness minerals?

Calcium, manganese and magnesium are the most common.

How do you Measure Hardness?

Parts per million or grains per gallon are the most common. One part per million (PPM) is just what it says: out of one million units, one unit. Grains, or grains per gallon (GPG) is a weight measurement taken from the Egyptians; one dry grain of wheat, or about 1/7000 of a pound. It takes 17.1 PPM to equal 1 GPG.

Why Should Hard Water Concern Me?

For many uses, it would not matter. For instance, to put out fires, water your lawn, wash the mud off the streets or float your boat, water would have to be pretty hard to cause a problem. But for bathing, washing dishes and clothes, shaving, washing your car and many other uses of water, hard water is not as efficient or convenient as "soft water." For instance:

  • you use only 1/2 as much soap cleaning with soft water.
  • because hard water and soap combine to form "soap scum" that can't be rinsed off, forming a 'bathtub ring' on all surfaces and drys leaving unsightly spots on your dishes.
  • when hard water is heated, the hardness minerals are re-crystallized to form hardness scale. This scale can plug your pipes and hot water heater, causing premature failure, and costly replacement.
  • the soap scum remains on your skin even after rinsing, clogging the pores of your skin and coating every hair on your body. This crud can serve as a home for bacteria, causing diaper rash, minor skin irritation and skin that continually itches.
  • for many industrial uses, the hardness minerals interfere with the process, causing inferior product.

Who Will Test My Water for Hardness?

If you are connected to a municipal supply, call the water Superintendent, or City Hall. They can either provide the answer, or direct you to the proper individual. Remember the conversion factor: it takes 17.1 PPM to equal 1 GPG. In other words, if your water has 171 PPM calcium in it, divide 171 by 17.1 to get the answer in grains. This example would be 10 grains, or GPG.

If you are on a private supply, you could contact your county extension agent: collect a sample in an approved container and send to the city or state health department for testing: find a testing lab (try the yellow pages): call a water conditioning company. By the way, if you are on a private well, YOU, AND YOU ALONE are responsible for the safety of the water you and your family drink. You should test your supply for bacteria at least once per year and other contaminants at least every three years -- more under certain conditions.

My Water is Hard; Now What?

If your water tests over 3 GPG hard, you should mechanically soften it. Softening water that is less than 3 GPG, while it makes your shaving and bathing more comfortable, is considered a luxury due to the fact that the cost is more than your savings. Over 3 GPG, you will save enough to pay for the cost and maintenance of a water conditioner.

As of this writing, the most economical way for you to soften your household water is with an ion exchange water softener. This unit uses sodium chloride (salt) to recharge man made plastic like beads that exchange hardness minerals for sodium. As the hard water passes through and around the plastic like beads, the hardness minerals (ions) attach themselves to the bead, dislodging the sodium ions. This process is called "ion exchange". When the plastic bead, called Resin, has no sodium ions left, it is exhausted, and can soften no more water. The resin is recharged by flushing with salt water. The sodium ions force the hardness ions off the resin beads; then the excess sodium is rinsed away, and the resin is ready to start the process all over again. This cycle can be repeated many, many time before the resin loses it's ability to react to these forces.

Which Water Conditioning Company should I call?

As in any purchase, talk to your friends and neighbors -- who do they use? Are they happy with them? Check with the Better Business Bureau for complaints. The BBB can't prevent shady business, but they can and do keep a file of complaints filed by people who have had dealings with them. Remember, just because the unit or Company carries a brand name is not any indication that the unit is any better.........but it may mean it is more costly for you!

Ask at least two to come to your home to look at your plumbing and then give you a quote on their equipment. Have them explain all the features of the unit, as well as the warranty.

What Should I look for in a Water Conditioner?

Make sure the unit has enough resin to treat all the water you and your family will use. As of this writing, the average usage per day, per person (including children), for inside the house is 87 gallons. You should also be shown two or three ways to initiate recharging the unit.

The oldest way is by a time clock, i.e., your water usage is calculated and the frequency of recharging programmed into the timer. On the appointed day, at the appointed hour, the unit recharges. If all went as calculated, ok. If you were gone -- too bad -- you just wasted salt and water. If you had extra company -- too bad -- you ran out of soft water. You must pick a unit that will treat one days supply of water and still have about 40% of the resin in the recharged state. This will provide you with the most efficiency for salt and regeneration water.

A second way to initiate recharge is by electronic sensing. By electronically checking the resin, these units can determine when the resin needs to be recharged -- this is a great help when your water hardness changes, when you have extra company or when you are gone for a few days. These 'sensor' units can save you up to 42% of your salt and recharge water as well as keep you in soft water when you have extra guests.

A third way to initiate recharge is by using a meter. These units have a meter installed in the water line and simply measure how many gallons of water you actually used. The unit is set according to your water hardness, and will recharge when the gallons used approach exhaustion of the resin bed, saving you a high percentage of your recharge salt and water.

Many variations of these methods are on the market. Some use computers to calculate in advance, when to recharge the unit; some have two resin beds (tanks), and switch back and forth between the two, keeping you in soft water all the time, at the highest efficiency. These systems are most effective in high hardness waters, i.e., over 10-12 GPG, and over 4 people in the family. Low hardness water and smaller families do not require the extra expense of these options.

I Have a Water Conditioner, Now my Water Feels "Slimy"

When the hardness minerals are removed, soap no longer forms a soap curd, or "bathtub ring" on your skin, plugging your pores, clinging to every strand of hair. You are now truly clean. That slick, slimy feeling you feel is your natural body oils -- without the soap scum. The old saying that you get "squeaky clean" is a myth; that feeling was caused by the soap scum on your skin. By the way, that soap scum provided an excellent place for bacteria to hide and grow, causing numerous minor skin ailments.

Water that Smells

My Water Stinks! What can I Do?

First, you must learn a little about your nose: Once you smell some things, your sense of smell is dulled for a short while, and you can't make accurate judgments of smell. For instance, if I blindfold you, let you smell gasoline, hand you a piece of onion to eat and tell you it is an apple, you can't tell it's not because your nose isn't working properly!! (Your sense of taste isn't working either -- smell and taste are closely related and affect each other!)

So, to correctly analyze your problem, you need to become a detective. The best time to locate the smell is after you have been away from home for a few hours -- this allows your nose to become sensitive to "that smell" again. With your 'sensitized' nose, go to an outside spigot -- one that the raw, untreated water flows from. Turn it on, let it run a few minutes, then smell it. If it smells -- we found it. If not, we must look further. (Many, many smells are not in the raw water at all, they are introduced into the water inside the house.) Go to a cold, treated water spigot inside the house, turn it on and let it run a minute; then smell. If this water smells, and the outside, untreated water didn't -- you must have a device (cartridge filter, water softener, etc.) in the water line that needs to be cleaned and sanitized.

If it is a cartridge, or 'string' filter, replace the element and sanitize the housing. If you have a water conditioner call the Company where you bought the unit for advise on how to sanitize the unit. If you rent the unit, just call! You can sanitize the unit by pouring Hydrogen Peroxide or Chlorine Bleach in the brine well of the salt tank, and placing the unit into regeneration. Check with the seller, or, if they are no longer in business, any Professional Water Conditioning Dealer for how much to put in your particular unit.

If the cold, treated water inside didn't smell, turn on the hot water and let it run a few minutes -- does it smell? If it does, chances are you have a sacrificial anode inside your hot water heater that is "coming apart at the seams" and throwing off a "rotten egg" odor. This obnoxious smell will drive you right out of your shower! The only solution is to remove the anode from the heater, voiding your warranty, or replace it with a new one made with aluminum alloy. This anode is placed in a (glass lined) hot water heater to seal up any cracks in the glass lining and prevent corrosion of the heater tank. You will find the anode on the top of the heater; remove the tin cover and insulation -- look for what looks like a pipe plug -- about 3/4 inch in size with a 1 1/16"fitting. Turn off the heat source and the water; have someone hold the tank to prevent it from turning, and unscrew the "plug". You will find that the 'plug' has a 30 - 40" long pipe (or what's left of one) attached to it. Hopefully, most of the rod is still attached -- just corroded. Replace that plug with a pipe plug and throw the anode away. If part of the rod has corroded off, and fallen into the heater, you may have to try to fish it out. (Good Luck!!) Either way, before you plug the hole, pour about 2 pints of chlorine bleach into the tank. This will kill the smell left in the heater. If, after a week or so, the smell returns, you must fish out the rod that is in the bottom of the tank. The bad news is that by removing the anode, your water heater warranty may be voided. Good Luck!

OK, It's my Raw Water That Smells -- Now What?

First, you must determine what is causing the smell, and how strong it is.

Minor, musty smell:

If it is a minor, or low-level smell, you MIGHT be able to solve it with a small, point-of-use carbon filter. You can place these types of filters on the water line going to the cold water where you draw you drinking water. Or, you might solve it with a whole-house filter on your incoming water line to filter all of the water inside your home.

Because carbon removes smells by ADsorbtion, i.e., the smell "sticks" or "adheres" to the carbon particles, you must be careful not to exceed the manufactures recommended flow -- some filters even have a flow restriction built in them. If you run water through them too fast, you will not remove the smells. Whenever you place a carbon filter in your water line, you must be sure to replace the element and sanitize the housing on a regular basis. Carbon filters remove organics from water, and the bacteria found in water like to eat organics -- the carbon filter is a nice, dark place, just full of food for them to grow and reproduce in. Regular and routine replacement will help prevent any buildup of bacteria in the cartridge.

Strong, rotten-egg smell:

Strong, rotten-egg odors in the raw water is usually the result of the decomposition of decaying underground organic deposits. As water is drawn to the surface, hydrogen sulfide gas can be released to the atmosphere. In strong concentrations, this gas is flammable and poisonous. It rapidly tarnishes silver, turning it black. It is toxic to aquarium fish in sufficient quantities. As little as 0.5 ppm hydrogen sulfide can be tasted in your drinking water.

Strong, musty smell:

If you are unlucky enough to have this problem, you should look for a company that has local experience in dealing with this problem. There are three basic ways to solve this problem for homeowners.


Installation of a whole house filter loaded with a media that is specific for hydrogen sulfide removal is successful many times. These types of filters must be recharged with chlorine or potassium permanganate. The removal capacities of these types of filters are usually fairly low, and must be sized to contain enough media to prevent premature exhaustion, and subsequent passage of the smell to service. It is also typical that the amount of hydrogen sulfide can fluctuate rapidly, causing great difficulty in sizing the unit. In addition, potassium permanganate is extremely "messy", and will leave stains that are very difficult to remove.


Feeder systems consist of a small pump that injects small amounts of chlorine (usually) into the incoming water. The water must then be held for a short period of time to allow the hydrogen sulfide to precipitate out of the water. This tank should be designed in such a manner that the water that enters it will mix thoroughly with the water in the tank, to assure complete reaction. The water then should pass through a filter to remove both the precipitated matter and the chlorine remaining in the water. You should be aware, however, that whenever you mix chlorine with organic materials (remember where hydrogen sulfide come from!), the chances are very high that trihalomethanes (possible cancer causing cragginess) will be formed. Also, feeder maintenance is high, you should be prepared to "play" with the unit frequently.


Aeration consists of breaking the incoming water into small droplets (spray) into the air, drawing fresh air through that spray, collecting the water into a storage tank, repressurize the water, passing it through a particulate filter to catch any particles that might be carried out of the storage tank. The air drawn though the spray must be vented outside the house -- remember, it is toxic and explosive. Although this system necessitates another pump to repressurize your supply, you are not adding any chemicals to your water, which makes it attractive. This system is low maintenance and no chemicals to purchase. Initial cost may be higher, however, and space requirements may be greater.

Aquacheme : Water Treatment Specialist

Industrial Water Treatment

Industrial Water Treatment can be classified into the following categories:

* Boiler water treatment
* Cooling water treatment
* Wastewater treatment

Water treatment is used to optimize most water-based industrial processes, such as: heating, cooling, processing, cleaning, and rinsing, so that operating costs and risks are reduced. Poor water treatment lets water interact with the surfaces of pipes and vessels which contain it. Steam boilers can scale up or corrode, and these deposits will mean more fuel is needed to heat the same amount of water. Cooling towers can also scale up and corrode, but left untreated, the warm, dirty water they can contain will encourage bacteria to grow, and Legionnaires' Disease can be the fatal consequence. Domestic water can become unsafe to drink if proper hygiene measures are neglected.

In many cases, effluent water from one process might be perfectly suitable for reuse in another process somewhere else on site. With the proper treatment, a significant proportion of industrial on-site wastewater might be reusable. This can save money in three ways: lower charges for lower water consumption, lower charges for the smaller volume of effluent water discharged and lower energy costs due to the recovery of heat in recycled wastewater.

Industrial water treatment seeks to manage four main problem areas: scaling, corrosion, microbiological activity and disposal of residual wastewater. Boilers do not have many problems with microbes as the high temperatures prevents their growth.
Scaling occurs when the chemistry and temperature conditions are such that the dissolved mineral salts in the water are caused to precipitate and form solid crystalline deposits. These can be mobile, like a fine silt, or can build up in layers on the metal surfaces of the systems. Scale is a problem because it insulates and heat exchange becomes less efficient as the scale thickens, which wastes energy. Scale also narrows pipe widths and therefore increases the energy used in pumping the water through the pipes.
Corrosion occurs when the parent metal oxidises (as iron rusts, for example) and gradually the integrity of the plant equipment is compromised. The corrosion products can cause similar problems to scale, but corrosion can also lead to leaks, which in a pressurised system can lead to catastrophic failures.

Microbes can thrive in untreated cooling water, which is warm and sometimes full of organic nutrients, as wet cooling towers are very efficient air scrubbers. Dust, flies, grass, fungal spores and so on collect in the water and create a sort of "microbial soup" if not treated with biocides. Most outbreaks of the deadly Legionnaires' Disease have been traced to unmanaged cooling towers, and the UK has had stringent Health & Safety Guidelines concerning cooling tower operations for many years as have had governmental agencies in other countries.

Disposal of residual wastewaters from an industrial plant is a difficult and costly problem. Most petroleum refineries, chemical and petrochemical plants have onsite facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the local and/or national regulations regarding disposal of wastewaters into community treatment plants or into rivers, lakes or oceans.

Sand Filters

Sand based water filters have been used for over 100 years to treat waste water. They are generally used on a larger scale to treat a water supply for a whole community, and will be custom made. Most units require a constant flow of water to work correctly, and so wouldn't be suitable for well water treatment.

Friday, September 5, 2008

Magnetic Water Conditioners

Electromagnetic water conditioners are a relatively new invention. The idea is that by passing water through a magnetic field, the calcium and magnesium ion's are altered in such a way that they loose their ability to cause scale.

This has a number of benefits; although the water is not technically soft, it has the useful properties of soft water, that is, it won't cause limescale in your pipes thus increasing heating efficiency and lengthening the lifespan of any clothes washed in the conditioned water.

Calcium is an important dietary element, so the fact that conditioned water still retains its calcium content is an added benefit.

Water Treatment

Water Treatment describes the processes used to make water more acceptable for a desired end-use. These can include use as drinking water, for use in industrial processes or to allow discharge into the environment without adverse ecologcal impact. These processes may be physical such as settlement, chemical such as disinfection or coagulation or biological such as lagooning, slow sand filtration or activated sludge.

Water Purification is the removal of contaminants from untreated water to produce drinking water that is pure enough for human consumption. Substances that are removed during the process of drinking water treatment include bacteria, algae, viruses, fungi, and man-made chemical pollutants. Many contaminants, such as man-made chemicals and heavy metals, can be dangerous—but depending on the quality desired, some are removed to improve the water's smell, taste, and appearance. There really is no such thing as pure water. As the universal solvent, the moment that purified water is exposed to the environment it interacts, even with carbon dioxide in the air. Water purification therefore is a process describing the treatments employed to meet the objectives of the user.

Sewage Treatment is the process that removes the majority of the contaminants from wastewater or sewage and produces both a liquid effluent suitable for disposal to the natural environment and a sludge. To be effective, sewage must be conveyed to a treatment plant by appropriate pipes and infrastructure and the process itself must be subject to regulation and controls. Some wastewaters require different and sometimes specialised treatment methods. At the simplest level, treatment of sewage and most wastewaters is through separation of solids from liquids, usually by settlement. By progressively converting dissolved material into solids, usually a biological floc which is then settled out, an effluent stream of increasing purity is produced.

Water Softening

A water softener reduces the calcium or magnesium ion concentration in hard water. These "hardness ions" cause two major kinds of problems. The metal ions react with soaps and calcium sensitive detergents, hindering their ability to lather properly and forming an unsightly precipitate— the familiar scum or "bathtub ring". Presence of "hardness ions" also inhibits the cleaning effect of detergent formulations. More seriously, calcium and magnesium carbonates tend to adhere to the surfaces of pipes and heat exchanger surfaces. The resulting scale buildup can restrict water flow in pipes. In boilers, the deposits act as thermal insulation that impedes the flow of heat into the water; this not only reduces heating efficiency, but allows the metal to overheat which, in a pressurized system, can lead to failure.

Conventional water-softening devices intended for household use depend on an ion-exchange resin in which "hardness" ions trade places with sodium ions that are electrostatically bound to the anionic functional groups of the polymeric resin. A class of minerals known as zeolites also exhibits ion-exchange properties; these minerals were widely used in earlier water softeners.

Water softeners are typically used when water is supplied from wells. Usually public water systems have low hardness so individual consumers need not have their own water softening equipment.

How It Works

The water to be treated passes through a bed of the resin. Negatively-charged resins absorb and bind metal ions, which are always positively charged. The resins initially contain univalent sodium ions, which exchange with divalent calcium and magnesium ions in the water. This exchange eliminates precipitation and soap scum formation.

As the water passes through both kinds of resin, the hardness ions replace the sodium which are released into the water. For most purposes, the low levels of salt in the treated water are innocuous. However because of the increase in sodium concentration, some people believe water softened in this way is not suitable for regular consumption.

As these resins become converted to their Ca2+ form they gradually lose their effectiveness and must be regenerated. This is done by passing a concentrated brine solution through them, causing the above processes to be reversed. This is a drawback, since most of the salt used for regeneration gets flushed out of the system and may be released into the soil or sewer. This can be damaging to the environment, especially in arid regions. For this reason, many jurisdictions prohibit such release and require users to dispose of the spent brine at an approved site or to use a commercial service company.

Water Filters

It may be useful to invest in a water filter for your home to make sure that your drinking water is clean and free from contaminants. There are different forms of water filters available today, all useful as a water softening treatment:

  • Granulated, activated carbon water filters – These are portable filters that are found in water jugs. They are the most simplest type of filter and removes contaminants such as chlorine, large particles and parasites. They are available at most kitchenware stores and are reasonably cheap if you have a low budget. However, they have a short filter life and don’t filter out many chemicals and bacteria.

  • Carbon block, activated carbon water filters – These types of filters are generally built-in to the water supply in your home. These filters are more expensive than granulated types, but they do give better filtration and do not need to be replaced as often.

  • Ceramic carbon water filters – This type of filter is comprised of a ceramic part and a carbon part, this gives it an ability to filter out a broad range of contaminants from the water supply. Some are infused with silver, as this is a good antibiotic and reduces the number of micro-organisms present. These filters are good value for money. They are built-in to the home water supply and need to be replaced about every 12 months in the average household.

  • Reverse osmosis water filters – These filters are often considered the best form of water filtration available today. The water is passed through a semi-permeable membrane, which filters out almost every contaminant. They are more expensive than other types of filters but have reasonably low running costs, effective filtration and can be used to filter water to the whole house.

  • Combination Systems – This filter has become available in recent years and are seen as an alternative to reverse osmosis systems. They have a number of different filters, and each filtration process removes different contaminants.

  • Alkaline Water Machines – This system not only filters your drinking water but it makes it more alkaline. It is a good system for those with environmental illnesses where there is too much acid in the body. It has effective filtration but it can be expensive and it wastes a lot of water during the filtration process.

Improving your Drinking Water

Filters; what can they do?

There are many types of filters available in the market place today. I will try to group them by the method they use to filter water. Almost everyone has seen the ads for the filter that fits on the end of your kitchen sink or bathroom spigot. These filters usually use two basic types of filtration: a filter 'pad' catches the large (usually over 25 micron in size) particles or 'chunks' , and a small amount of carbon to adsorb organics and/or chlorine. The main problem here is the flow rates at which they are expected to work at. The consumer expects to turn the tap on as normal and draw "filtered" water. To remove free chlorine, for instance, standard engineering practices set the maximum flow rate at 10 gallons per minute per square foot (144 square inches) of surface area of the carbon, *if* you are using a standard 30" bed depth. To remove chloramines or organics, the maximum flow rate is set at 5 gallons per minute per square foot of surface area. If your spigot will provide a flow of 1.5 gallons per minute, what size filter do you need hanging on the end of that spigot to insure that the chlorine and organics will not be swept past through the filter, into your glass? If you purchase this type of filter, make sure it has a way of limiting the rate at which water passes through it.

Next comes the cartridge type filter. Most common are the 10 1/2 or 20 inch long filters. This type filter will usually have a removable housing, into which different types of "elements" can be placed. A sediment filter cartridge element can be manufactured to remove certain size particles and larger. Most elements for home use will indicate 30 or 50 micron and larger removal. More expensive elements, usually for industrial use, may indicate a particle size (in microns) and add the words "Absolute" after it. No, it isn't Vodka, it simply means that if it says 5 micron absolute, it means it! Very few particles larger than 5 microns will pass through the filter. The regular filter may say 25 microns, meaning that *most* of the particles 25 microns and larger will be caught by the filter. Remember, there filters actually get better, or more effective, as they are used. The 'junk' in the water collects on the surface of the filter and becomes a part of the filter as well. As it builds up, progressively smaller and smaller particles are trapped, and the flow rate through the filter slowly diminishes. This slowing of the flow rate can be a source of problems to water using appliances in your home. If you use such a filter, regular changing of the filter element is very important. Elements for these filters can also be carbon (block or granular, or powdered), can be manufactured for use in hot water, can be ceramic, pleated as well as many other configurations. Some manufacturers are mixing a small amount of silver into the carbon to help prevent any bacteria growth in them. This has yet to be a proven methodology. In fact, make sure that such a filter doesn't give off more silver than is allowed, if not rinsed thoroughly prior to use, especially after a prolonged period of non-use. Remember, all filters, carbon especially, trap organics that bacteria feed on, and as the water sits without moving, they can multiply rapidly. Always change the elements on a regular, frequent basis.

Selective Resins

A relative newcomer to the market, some small filters now contain resins that only remove specific things from the water, such as Nitrates, Fluoride or Lead. Technology is rapidly changing in this area; If you have a need for such a device, you should ask for supporting test results from an independent testing lab to verify that the unit will perform as advertised. Many states now have legislation that requires such data be provided to you prior to purchase.

Used mainly in labs, manufacturing processes, or for serious aquarium owners, DI filters are actually more complex than a filter. True filters, unlike the selective resin and DI units, work on a mechanical basis: they just 'catch' the particles that are too large to fit through the spaces between the filter media. (Well, I fibbed a little; but who wants to know about the Van Der Waals or Coulomb forces?) DI works by ion exchange, just like a water softener. Just as a water softener exchanges sodium for hardness minerals, a DI unit will have two types of resin in it: Cation and Anion. Basically, the Cation resin (like in a water softener) removes the ions with a positive charge, while the Anion resin removes those ions with a negative charge. Instead of using salt as a regenerant, acid and caustic are used. Some small DI cartridges are sold as "throw-aways", others can be returned for regeneration and reuse. These small units can treat only small amounts of raw, city water. Usually, it is much more economical to pre-treat the water feeding a DI system with reverse osmosis water.


One of the oldest methods for cleaning water is distillation. Simply put, you boil water, catch the steam, and condense it back into water. Theory is, the minerals stay behind in the boiling chamber, and only *pure* water ends up in your container. In the real world, most of those things do happen; but if you do not perform preventative maintenance on your still, you can get very poor results. Distillation will kill bacteria, viruses, cysts as well as remove heavy metals, organics, radionuclides, inorganics and particulates if properly maintained. One thing you must watch out for is VOC's (volatile organic chemicals). These chemicals have a lower boiling point than water (like benzene), and can vaporize and mix with the steam, carrying over into the product water. Some stills today have a volatile gas vent -- a small hole at the top of the condensing coil that allows the venting of such substances. Many distillers have a carbon filter to "polish" the product water before use and to remove any VOC's that may carry over. The energy used to treat a gallon of water is usually about 3,000 watts, or about 25 cents per gallon (average) in the US. This treatment method requires that you 'plan ahead' and make and store water for use, which makes it somewhat less appealing. The more elaborate units will make and store water automatically, but raise the initial investment and maintenance of the equipment.

Reverse Osmosis

This is a process that is often described as filtration, but it is far more complex than that. We sometimes explain it as a filter because it is much easier to visualize using those terms. We should remember that osmosis is how we feed each cell in our bodies: As our blood is carried into the smallest of capillaries in our bodies, nutrients actually pass through the cell wall to sustain it's life. Reverse osmosis is just the opposite: We take water with "nutrients" (in this case, junk) in it, and apply pressure to it against a certain type of membrane, and, presto -- out comes "clean" water. Lets review the basics: If you take a jar of water and place a semi-permeable membrane (like a cell wall? or a piece of skin?) in it, dividing the jar into two sections, then place water in both sides to an equal level, nothing happens. But, if you place salt (or other such substance) into one side of the jar, you will notice that, after awhile, the water level in the salty side begins to rise higher as the unsalted side lowers. This is osmotic pressure at work: The two solutions will continue to try to reach the same level of salt in each side by the unsalted water passing through the membrane to dilute the salty water. This will continue until the "head" pressure of the salt water overcomes the osmotic pressure created by the differences in the two solutions. Researchers have discovered that if we take that membrane and feed water with sufficient pressure to overcome the osmotic pressure of the two waters, we can 'manufacture' clean water on the side of the membrane that has no pressure. We sometimes say we "filter" the water through the membrane. Depending on the membrane design, and the material it made from, the amount of TDS (total dissolved solids) reduction will range from 80 to over 99 per cent. Different minerals have different rejection rates, for instance, the removal rate for the membrane I am looking at now is 99.5% for Barium and Radium 226/228; but only 85.9% for Fluoride and 94.0% for Mercury. Removal rates are very dependent on feedwater pressures, and some membranes are not tolerant to high or low pH. For home use, it is important to make sure you get an RO *System*; i.e., a sediment pre-filter, a carbon pre-filter, membrane, storage tank and post carbon filter. Some of these filters may be combined into one, i.e., the pre-filter may be both a particulate and a carbon filter. A lot of comments have been made concerning the *wasting* of water by an RO. True, the old style units with the early type membranes were more prone to becoming plugged, or fouled by the "junk" they removed from the water. To help keep this from happening, a small amount of water was allowed to run across the membrane to help carry away those impurities to drain. Early designs only recovered 1 gallon of good water for every 4-8 gallons used to keep the membrane clean. And when your storage tank was full, water still ran to the drain because the early membranes were made of a material that the little bugs in your water supply (no, not pathogens, or dangerous to you in small numbers) loved to eat! So to prevent that, we just let the water run so they couldn't have time to stop and eat. :>) Now membranes are made that not only recover a much higher percentage of the feedwater, but the bugs don't eat them! Newer systems not only recover more water to begin with, they may also have a shut off device that stops all water flow when the storage tank is full. Actual recovery rate is dependent on several factors, including the TDS, and just what the TDS is composed of, in your feedwater. Temperature, pressure also have a big effect on the amount of product water you can make in a given period. Remember, all RO units are normally rated using a feedwater temperature of 77 degrees F -- is your feed water temperature that high?

What is the best water for Coffee?

Well, that a good question! After visiting with many coffee people, I have gathered the following as a basis for recommending the "perfect water" for coffee.

1. All oxidants removed. (Chlorine or other such "sanitizers".)

2. All organics removed. (You know, dead fish, tadpoles, THM's, insecticides, pesticides, etc.)

3. TDS (total dissolved solids) from 60 to 100 ppm (parts per million)

4. Hardness of about 3-4 grains per gallon. (51.3 to 68.4 ppm)

5. Low sodium water, i.e., less than 10 mg/L.

6. pH depends on the Bean you are using, plus the method of extraction.

7. Iron, Manganese and copper gone, or less than 0.02 ppm.

What is the best way to get this type of water?

There is no single answer for this question, however, if we assume you are getting your water from a municipal supply, we *assume* the Iron and Manganese problems are taken care of by the city plant. (Some towns may not solve these problems -- you be the judge!) Copper *may* come from the supply itself, or, if the water is aggressive enough, it may actually be picked off the copper plumbing in your house as it sits overnight in the pipes. (Lead can also be leached out of the older "sweat" joints that may have used solder that contained lead.) It is best to "clear the pipes" the first thing in the morning before using any water for ingestion. Simply run enough water to clear your pipes of the 'overnight' standing water that *may* have picked up the harmful metals from your pipes -- use it to water your houseplants. If we use a good, properly sized carbon filter, we will substantially reduce the organics and oxidants in the water, as well as remove most of the particulates. However, we still have TDS and Hardness to worry about. If we soften the water, we do not reduce the TDS, we simply *exchange* the hardness minerals for Sodium -- which we don't want for coffee! The best answer (usually) is the reverse osmosis system. This *system* usually has a particulate and carbon filter (organics, oxidants and particulates are reduced); and a membrane (reduces the TDS by about 90% -- including hardness, sodium and others as well); all linked together in one flow path.

We can greatly improve the coffee by using any one of the above mentioned methods, but if we combine them, we get, for all practical purposes, the *best* water for your coffee! Rule of thumb: With an RO System, whatever impurities were in the water are typically reduced by 90% or more, leaving only water behind, which is what we really wanted, anyway!

How much sodium does Ion Exchange add to my water?
For every grain of hardness in your water, 7.5 mg of Sodium will be *added* to each quart of water by the ion-exchange method. If you have water that is 10 grains per gallon hard; you will add 75.0 mg of Sodium per quart of water softened by ion-exchange. To put that in perspective, one 8 oz glass of milk contains 120 mg of Sodium, one slice of white bread contains 114 mg of Sodium. You must also remember that there is *probably* Sodium in the raw water, too. If your city supply treats your water by a "hardness reduction" treatment plant, you can be sure that the Sodium level in your water has increased as a result -- how much? Call your plant operator and ask -- it is information free to the public.

Reverse Osmosis

In water filter terms, reverse osmosis (or hyper-filtration) is the process of filtering water under pressure through a semi-permeable membrane, allowing water to pass through but rejecting other particles such as bacteria, toxins, salts, and anything bigger than around 150 Daltons.

What is RO (Reverse Osmosis)?

Reverse Osmosis is water filterization system using Membrane Filter with numerous tiny holes so that it could filter metal liquid and virus. When passing through the filter, they will stick to the surface of Membrane Filter (The water for this Membrane filter process must be water without suspended solids. And before passing through Membrane filter, it has to pass through 3 types of normal filter.) So, the water needs to get an appropriate amount of force from booster pump to be able to pass through Membrane Filter (Typically Membrane filter allows only small water molecule passing through but not bacteria, virus and metal liquid with complicated molecule). The detect particle is gotten rid of in form of waste water while the purified water will be filtered again by activate Carbon to make sure that water from Reverse Osmosis is clean and clear.

Aquacheme : Water Treatment Specialist

Water Purification

Water purification is the removal of contaminants from raw water to produce drinking water that is pure enough for human consumption or for industrial use. Substances that are removed during the process include parasites ( such as Giardia or Cryptosporidium) , bacteria, algae, viruses, fungi, minerals (including toxic metals such as Lead, Copper etc.), and man-made chemical pollutants. Many contaminants can be dangerous—but depending on the quality standards, others are removed to improve the water's smell, taste, and appearance. A small amount of disinfectant is usually intentionally left in the water at the end of the treatment process to reduce the risk of re-contamination in the distribution system.

Many environmental and cost considerations affect the location and design of water purification plants. Groundwater is cheaper to treat, but aquifers usually have limited output and can take thousands of years to recharge. Surface water sources should be carefully monitored for the presence of unusual types or levels of microbial/disease causing contaminants. The treatment plant itself must be kept secure from vandalism and terrorism.

It is not possible to tell whether water is safe to drink just by looking at it. Simple procedures such as boiling or the use of a household charcoal filter are not sufficient for treating water from an unknown source. Even natural spring water—considered safe for all practical purposes in the 1800s—must now be tested before determining what kind of treatment is needed.

Sources of Drinking Water
1. Deep groundwater: The water emerging from some deep groundwaters may have fallen as rain many decades or even hundreds of years ago. Soil and rock layers naturally filter the groundwater to a high degree of clarity before it is pumped to the treatment plant. Such water may emerge as springs, artesian springs, or may be extracted from boreholes or wells. Deep groundwater is generally of very high bacteriological quality (i.e., a low concentration of pathogenic bacteria such as Campylobacter or the pathogenic protozoa Cryptosporidium and Giardia) but may be rich in dissolved solids, especially carbonates and sulphates of calcium and magnesium. Depending on the strata through which the water has flowed, other ions may also be present including chloride, and bi-carbonate. There may be a requirement to reduce the iron or manganese content of this water to make it pleasant for drinking, cooking, and laundry use. Disinfection is also required. Where groundwater recharge is practised, it is equivalent to lowland surface waters for treatment purposes.

2. Shallow groundwaters: Water emerging from shallow groundwaters is usually abstracted from wells or boreholes. The bacteriological quality can be variable depending on the nature of the catchment. A variety of soluble materials may be present including potentially toxic metals such as zinc and copper. Arsenic contamination of groundwater is a serious problem in some areas, notably from shallow wells in Bangladesh and West Bengal in the Ganges Delta.

3. Upland lakes and reservoirs: Typically located in the headwaters of river systems, upland reservoirs are usually sited above any human habitation and may be surrounded by a protective zone to restrict the opportunities for contamination. Bacteria and pathogen levels are usually low, but some bacteria, protozoa or algae will be present. Where uplands are forested or peaty, humic acids can colour the water. Many upland sources have low pH which require adjustment.

4. Rivers, canals and low land reservoirs: Low land surface waters will have a significant bacterial load and may also contain algae, suspended solids and a variety of dissolved constituents.

5. Atmospheric water generation is a new technology that can provide high quality drinking water by extracting water from the air by cooling the air and thus condensing water vapour.

6. Rainwater harvesting or fog collection which collect water from the atmosphere can be used especially in areas with significant dry seasons and in areas which experience fog even when there is little rain .

Stages in typical municipal water treatment

There are three principal stages in water purification:-

1. Primary treatment - Collecting and screening including pumping from rivers and initial storage
2. Secondary treatment - removal of fine solids and the majority of contaminants using filters, coagulation, flocculation and membranes
3. Tertiary treatment - polishing, pH adjustment, carbon treatment to remove taste and smells, disinfection, and temporary storage to allow the disinfecting agent to work.

Primary Treatment

1. Pumping and containment - The majority of water must be pumped from its source or directed into pipes or holding tanks. To avoid adding contaminants to the water, this physical infrastructure must be made from appropriate materials and constructed so that accidental contamination does not occur.
2. Screening (see also Screen filter) - The first step in purifying surface water is to remove large debris such as sticks, leaves, trash and other large particles which may interfere with subsequent purification steps. Most deep Groundwater does not need screening before other purification steps.
3. Storage - Water from rivers may also be stored in bankside reservoirs for periods between a few days and many months to allow natural biological purification to take place. This is especially important if treatment is by slow sand filters. Storage reservoirs also provide a buffer against short periods of drought or to allow water supply to be maintained during transitory pollution incidents in the source river.
4. Pre-conditioning - Many waters rich in hardness salts are treated with soda-ash (Sodium carbonate)to precipitate calcium carbonate out utilising the common ion effect.
5. Pre-chlorination - In many plants the incoming water was chlorinated to minimise the growth of fouling organisms on the pipe-work and tanks. Because of the potential adverse quality effects (see Chlorine below), this has largely been discontinued.

Secondary treatment

There are a wide range of techniques that can be used to remove the fine solids, micro-organisms and some dissolved inorganic and organic materials. The choice of method will depend on the quality of the water being treated, the cost of the treatment process and the quality standards expected of the processed water.

1. pH adjustment - If the water is acidic, lime or soda ash is added to raise the pH. Lime is the more common of the two additives because it is cheaper, but it also adds to the resulting water hardness. Making the water slightly alkaline ensures that coagulation and flocculation processes work effectively and also helps to minimise the risk of lead being dissolved from lead pipes and lead solder in pipe fittings.

2. Coagulation and flocculation - Together, coagulation and flocculation are purification methods that work by using chemicals which effectively "glue" small suspended particles together, so that they settle out of the water or stick to sand or other granules in a granular media filter. Many of the suspended water particles have a negative electrical charge. The charge keeps particles suspended because they repel similar particles. Coagulation works by eliminating the natural electrical charge of the suspended particles so they attract and stick to each other. The joining of the particles so that they will form larger settleable particles is called flocculation. The larger formed particles are called floc. The coagulation chemicals are added in a tank (often called a rapid mix tank or flash mixer), which typically has rotating paddles. In most treatment plants, the mixture remains in the tank for 10 to 30 seconds to ensure full mixing. The amount of coagulant that is added to the water varies widely due to the different source water quality.

One of the more common coagulants used is aluminum sulfate, sometimes called filter alum. Aluminum sulfate reacts with water to form flocs of aluminium hydroxide.

Coagulation with aluminum compounds may leave a residue of aluminium in the finished water. This is normally about 0.1 to 0.15 mg/L. It has been established that Aluminium can be toxic to humans at high concentrations.

Iron(II) sulfate or iron (III) chloride are other common coagulants. Iron(III) coagulants work over a larger pH range than aluminum sulfate but are not effective with many source waters. Other benefits of iron(III) are lower costs and in some cases slightly better removal of natural organic contaminants from some waters. Coagulation with iron compounds typically leaves a residue of iron in the finished water. This may impart a slight taste to the water, and may cause brownish stains on porcelain fixtures. The trace levels of iron are not harmful to humans, and indeed provide a needed trace mineral. Because the taste and stains may lead to customer complaints, aluminium tends to be favoured over iron for coagulation.

Cationic and other polymers can also be used. They are often called coagulant aids used in conjunction with other inorganic coagulants. The long chains of positively charged polymers can help to strengthen the floc making it larger, faster settling and easier to filter out. The main advantages of polymer coagulants and aids are that they do not need the water to be alkaline to work and that they produce less settled waste than other coagulants, which can reduce operating costs. The drawbacks of polymers are that they are expensive, can blind sand filters and that they often have a very narrow range of effective doses.

3. Flocculation - In flocculation coagulants are used but the resultant floc is settled out rather than filtered through sand filters. The chosen coagulant and the raw water is slowly mixed in a large tank called a flocculation basin. Unlike a rapid mix tank, the flocculation paddles turn very slowly to minimise turbulence. The principle involved is to allow as many particles to contact other particles as possible generating large and robust floc particles. Generally, the retention time of a flocculation basin is at least 30 minutes with speeds between 0.5 feet and 1.5 feet per minute (15 to 45 cm / minute). Flow rates less than 0.5 ft/min cause undesirable floc settlement within the basin.

4. Sedimentation -Water exiting the flocculation basin enters the sedimentation basin, also called a clarifier or settling basin. It is a large tank with slow flow, allowing floc to settle to the bottom. The sedimentation basin is best located close to the flocculation basin so the transit between does not permit settlement or floc break up. Sedimentation basins can be in the shape of a rectangle, where water flows from end to end, or circular where flow is from the center outward. Sedimentation basin outflow is typically over a weir so only a thin top layer-furthest from the sediment-exits.The amount of floc that settles out of the water is dependent on the time the water spends in the basin and the depth of the basin. The retention time of the water must therefore be balanced against the cost of a larger basin. The minimum clarifier retention time is normally 4 hours. A deep basin will allow more floc to settle out than a shallow basin. This is because large particles settle faster than smaller ones, so large particles bump into and integrate smaller particles as they settle. In effect, large particles sweep vertically though the basin and clean out smaller particles on their way to the bottom.

As particles settle to the bottom of the basin a layer of sludge is formed on the floor of the tank. This layer of sludge must be removed and treated. The amount of sludge that is generated is significant, often 3%-5% of the total volume of water that is treated. The cost of treating and disposing of the sludge can be a significant part of the operating cost of a water treatment plant. The tank may be equipped with mechanical cleaning devices that continually clean the bottom of the tank or the tank can be taken out of service when the bottom needs to be cleaned.

An increasingly popular method of floc removal is by dissolved air flotation. A proportion of clarified water, typical 5-10% of throughput, is recycled and air is dissolved in it under pressure. This is injected into the bottom of the clarifier tank where tiny air bubbles are formed which attach themselves to the floc particles and float them to the surface. A sludge blanket is formed which is periodically removed using mechanical scrapers. This method is very efficient at floc removal and reduces loading on filters, however it is unsuitable for water sources with a high concentration of sediment.

5. Filtration - After separating most floc, the water is filtered as the final step to remove remaining suspended particles and unsettled floc. The most common type of filter is a rapid sand filter. Water moves vertically through sand which often has a layer of activated carbon or anthracite coal above the sand. The top layer removes organic compounds including taste and odour. The space between sand particles is larger than the smallest suspended particles, so simple filtration is not enough. Most particles pass through surface layers but are trapped in pore spaces or adhere to sand particles. Effective filtration extends into the depth of the filter. This property of the filter is key to its operation: if the top layer of sand were to block all the particles, the filter would quickly clog.

To clean the filter, water is passed quickly upward through the filter, opposite the normal direction (called backflushing or backwashing) to remove embedded particles. Prior to this, compressed air may be blown up through the bottom of the filter to break up the compacted filter media to aid the backwashing process; this is known as air scouring. This contaminated water can be disposed of, along with the sludge from the sedimentation basin, or it can be recycled by mixing with the raw water entering the plant.

Some water treatment plants employ pressure filters. These work on the same principle as rapid gravity filters differing in that the filter medium is enclosed in a steel vessel and the water is forced through it under pressure.

6. Slow sand filters may be used where there is sufficient land and space. These rely on biological treatment processes for their action rather than physical filtration. Slow sand filters are carefully constructed using graded layers of sand with the coarsest at the base and the finest at the top. Drains at the base convey treated water away for disinfection. Filtration depends on the development of a thin biological layer on the surface of the filter. An effective slow sand filter may remain in service for many weeks or even months if the pre-treatment is well designed and produces an excellent quality of water which physical methods of treatment rarely achieve.

7. Ultrafiltration membranes are a relatively new development; they use polymer film with chemically formed microscopic pores that can be used in place of granular media to filter water effectively without coagulants. The type of membrane media determines how much pressure is needed to drive the water through and what sizes of micro-organisms can be filtered out.

Tertiary treatment

Disinfection is normally the last step in purifying drinking water. Water is disinfected to destroy any pathogens which passed through the filters. Possible pathogens include viruses, bacteria, including Escherichia coli, Campylobacter and Shigella, and protozoans, including G. lamblia and other Cryptosporidia. In most developed countries, public water supplies are required to maintain a residual disinfecting agent throughout the distribution system, in which water may remain for days before reaching the consumer. Following the introduction of any chemical disinfecting agent, the water is usually held in temporary storage - often called a contact tank or clear well to allow the disinfecting action to complete.

1. Chlorine- The most common disinfection method is some form of chlorine or its compounds such as chloramine or chlorine dioxide. Chlorine is a strong oxidant that kills many micro-organisms.

Because chlorine is a toxic gas, there is a danger of a release associated with its use. This problem is avoided by the use of sodium hypochlorite, which is a relatively inexpensive solid that releases free chlorine when dissolved in water. Handling the solid, however, requires greater routine human contact through opening bags and pouring than the use of gas cylinders which are more easily automated. Both disinfectants are widely used despite their respective drawbacks. A major drawback to using chlorine gas or sodium hypochlorite is that they react with organic compounds in the water to form potentially harmful levels of the chemical by-products trihalomethanes (THMs) and haloacetic acids, both of which are carcinogenic and regulated by the U.S. Environmental Protection Agency (EPA). The formation of THMs and haloacetic acids is minimised by effective removal of as many organics from the water as possible before disinfection. Although chlorine is effective in killing bacteria, it has limited effectiveness against protozoans that form cysts in water. (Giardia lamblia and Cryptosporidium, both of which are pathogenic).

2. Chlorine dioxide is another fast-acting disinfectant. It is, however, rarely used, because it may create excessive amounts of chlorate and chlorite, both of which are regulated to low allowable levels. Chlorine dioxide also poses extreme risks in handling: not only is the gas toxic, but it may spontaneously detonate upon release to the atmosphere in an accident.

3. Chloramines are another chlorine-based disinfectant. Although chloramines are not as effective as disinfectants, compared to chlorine gas or sodium hypochlorite, they are less prone to form THMs or haloacetic acids. It is possible to convert chlorine to chloramine by adding ammonia to the water along with the chlorine: The chlorine and ammonia react to form chloramine. Water distribution systems disinfected with chloramines may experience nitrification, wherein ammonia is used a nitrogen source for bacterial growth, with nitrates being generated as a byproduct.

4. Ozone (O3) is a relatively unstable molecule of oxygen which readily gives up one atom of oxygen providing a powerful oxidising agent which is toxic to most water borne organisms. It is a very strong, broad spectrum disinfectant that is widely used in Europe. It is an effective method to inactivate harmful protozoans that form cysts. It also works well against almost all other pathogens. Ozone is made by passing oxygen through ultraviolet light or a "cold" electrical discharge. To use ozone as a disinfectant, it must be created on site and added to the water by bubble contact. Some of the advantages of ozone include the production of relatively fewer dangerous by-products (in comparison to chlorination) and the lack of taste and odor produced by ozonation. Although fewer by-products are formed by ozonation, it has been discovered that the use of ozone produces a small amount of the suspected carcinogen Bromate. Another one of the main disadvantages of ozone is that it leaves no disinfectant residual in the water. Ozone has been used in drinking water plants since 1906 where the first industrial ozonation plant was built in Nice, France. The U.S. Food and Drug Administration has accepted ozone as being safe; and it is applied as an anti-microbiological agent for the treatment, storage, and processing of foods.

5. UV radiation is very effective at inactivating cysts, as long as the water has a low level of colour so the UV can pass through without being absorbed. The main drawback to the use of UV radiation is that, like ozone treatment, it leaves no residual disinfectant in the water.

Because neither ozone nor UV radiation leaves a residual disinfectant in the water, it is sometimes necessary to add a residual disinfectant after they are used. This is often done through the addition of chloramines, discussed above as a primary disinfectant. When used in this manner, chloramines provide an effective residual disinfectant with very little of the negative aspects of chlorination.

Additional treatment options

1. Fluoridation -in many areas fluoride is added to water for the purpose of preventing tooth decay. This process is referred to as water fluoridation. Fluoride is usually added after the disinfection process. In the United States, fluoridation is usually accomplished by the addition of dihydrogen hexafluorosilicate, which decomposes in water, yielding fluoride ions.

2. Water conditioning: This is a method of reducing the effects of hard water. Hardness salts are deposited in water systems subject to heating because the decomposition of bicarbonate ions creates carbonate ions which crystalise out of the saturated solution of calcium or magnesium carbonate. Water with high concentrations of hardness salts can be treated with soda ash (sodium carbonate) which precipitates out the excess salts, through the common ion effect, as calcium carbonate of very high purity. The preciptated calcium carbonate is traditionally sold to the manufacturers of toothpaste. Several other methods of industrial and residential water treatment are claimed (without general scientific acceptance) to include the use of magnetic or/and electrical fields reducing the effects of hard water.

3. Plumbo-solvency reduction: In areas with naturally acidic waters of low conductivity (i.e surface rainfall in upland mountains of igneous rocks), the water is capable of dissolving lead from any lead pipes that it is carried in. The addition of small quantities of phosphate ion and increasing the pH slightly both assist in greatly reducing plumbo-solvency by creating insoluble lead salts on the inner surfaces of the pipes.

4. Radium Removal: Some groundwater sources contain radium, a radioactive chemical element, including many groundwater sources north of the Illinois River in Illinois. Radium can be removed by ion exchange, or by water conditioning. The back flush or sludge that is produced is, however, a low-level radioactive waste.

5. Fluoride Removal: Although fluoride is added to water in many areas, some areas of the world have excessive levels of natural fluoride in the source water. Excessive levels can be toxic. One method of reducing fluoride levels is through treatment with activated alumina.

Other water purification techniques

Other popular methods for purifying water, especially for local private supplies are listed below. In some countries some of these methods are also used for large scale municipal supplies. Particularly important are distillation (de-salination of seawater) and reverse osmosis.

1. Boiling: Water is heated hot enough and long enough to inactivate or kill microorganisms that normally live in water at room temperature. Near sea level, a vigorous rolling boil for at least one minute is sufficient. At high altitudes (greater than two kilometers or 5000 feet) three minutes is recommended. US EPA emergency disinfection recommendations In areas where the water is "hard" (that is, containing significant dissolved calcium salts), boiling decomposes the bicarbonate ions, resulting in partial precipitation as calcium carbonate. This is the "fur" that builds up on kettle elements, etc., in hard water areas. With the exception of calcium, boiling does not remove solutes of higher boiling point than water and in fact increases their concentration (due to some water being lost as vapour). Boiling does not leave a residual disinfectant in the water. Therefore, water that has been boiled and then stored for any length of time may have acquired new pathogens.

2. Carbon filtering: Charcoal, a form of carbon with a high surface area, absorbs many compounds including some toxic compounds. Water passing through activated charcoal is common in household water filters and fish tanks. Household filters for drinking water sometimes contain silver to release silver ions which have a bactericidal effect.

3. Distillation involves boiling the water to produce water vapour. The vapour contacts a cool surface where it condenses as a liquid. Because the solutes are not normally vaporised, they remain in the boiling solution. Even distillation does not completely purify water, because of contaminants with similar boiling points and droplets of unvaporised liquid carried with the steam. However, 99.9% pure water can be obtained by distillation. Distillation does not confer any residual disinfectant and the distillation apparatus may be the ideal place to harbour Legionnaires' disease.

4. Reverse osmosis: Mechanical pressure is applied to an impure solution to force pure water through a semi-permeable membrane. Reverse osmosis is theoretically the most thorough method of large scale water purification available, although perfect semi-permeable membranes are difficult to create. Unless membranes are well-maintained, algae and other life forms can colonise the membranes.

5. Ion exchange: Most common ion exchange systems use a zeolite resin bed to replace unwanted Ca2+ and Mg2+ ions with benign (soap friendly) Na+ or K+ ions. This is the common water softener.

6. Electrodeionization: Water is passed between a positive electrode and a negative electrode. Ion selective membranes allow the positive ions to separate from the water toward the negative electrode and the negative ions toward the positive electrode. High purity deionized water results. The water is usually passed through a reverse osmosis unit first to remove non-ionic organic contaminants.

Water purification for hydrogen production

For small scale production of hydrogen water purifiers are installed to prevent formation of minerals on the surface of the electrodes and to remove organics and chlorine from utility water. First the water passes through a 20 micrometre interference (mesh or screen filter) filter to remove sand and dust particles, second, a charcoal filter (activated carbon) to remove organics and chlorine, third stage, a de-ionizing filter to remove metallic ions. A test can be done before and after the filter for proper functioning on barium, calcium, potassium, magnesium, sodium and silicon.

Another used method is reverse osmosis.


* Masters, Gilbert M. Introduction to Environmental Engineering. 2nd ed. Upper Saddle River, NJ: Prentice Hall, 1998.
* United States EPA Ground and Drinking Water Homepage. EPA Ground and Drinking Water Homepage Visited 12/13/05
* Viessman, Warren, and Mark J. Hammer. Water Supply and Pollution Control. 7th ed. Upper Saddle River, NJ: Prentice Hall, 2005.