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.
