In 1972, the United States legislature passed the Clean Water Act due to a crisis in the nation’s water purity. The purpose of the act was to restore the chemical, biological, and physical nature of our nation’s waterways that had been so damaged by pollution. The goal of the act was that, by 1985, no more pollutants would be discharged into the water supply and all of our nation’s rivers, streams, and lakes would be fishable and swimmable once more. Every city was required to install a water treatment plant, and every industry was required to use the best available technology to limit the amount of pollutants that entered water sources (Outwater, 1996). Under these stringent demands, water quality began to improve slightly. Still, almost two decades after the year of supposed goal fulfillment, about a third of the nation’s waterways continue to be polluted.
There is no doubt that industrial sites have cleaned up their act. They would no longer be in business today if they had not. So, why is our nation’s water still so dirty? The answer is very simple. Water follows a natural cycle. It moves from the rain to the mountaintops, through streams and rivers to the sea, and then to the clouds once more. In the United States, the natural water cycle has been changed in a number of ways. Through dredging, damming, and tampering with or eliminating the ecological niches where water is able to clean itself, we have changed the pathways that water takes through the American landscape, greatly benefiting agriculture and the American economy. In the long run, we have ended up with dirty, impure water. Water treatment remains as the best available technology we have to rectify this problem.
Source: http://www.historyofwaterfilters.com/water-why-dirty.html