Under the act, EPA established the first national standards for community water supply systems. The Region has 3,590 community water systems, ranging from the vast New York City system, supplying drinking water for nine million people, to thousands of small systems, which can be as simple as a well servicing a handful of mobile homes. EPA determines the minimum level of treatment required. In addition, the Agency has set maximum allowable levels for 90 contaminants, ranging from nitrates and mercury to pesticides and benzene, which can be found in drinking water. And because lead is known to affect intellectual and behavioral development in children, EPA banned the use of lead pipe and lead solder.
All surface water is disinfected, usually with chlorine.
Much is also filtered, but a small number of municipalities that have protected their water sources have been able to avoid the cost of filtration. Because soil acts as a natural bacterial filter, most well and spring water does not require treatment. Some pollutants, however, make their way through the earth. One gallon of leaked or spilled gasoline can contaminate one million gallons of underground drinking water. Once contaminated, groundwater is difficult, often impossible to purify.