Public Water Treatment Overview
A BIT ABOUT WATER QUALITY
Surface water sources, such as lakes and rivers, are vulnerable to bacterial and chemical contamination as they often receive storm and agricultural runoff. In order to address these contamination concerns, the United States Environmental Protection Agency requires public water utilities using surface water to uphold a set of Surface Water Treatment Rules (SWTRs) to reduce illnesses caused by pathogens.
It is impossible to remove all substances from drinking water (including bottled water) with the currently available treatment technologies. However, drinking water treatment plants can greatly reduce chemical, microbial, and particulate contamination to produce water that meets rigorous drinking water regulations.
In municipal water systems, raw water is pumped from the source water (either groundwater aquifers, surface waters or both) into the water treatment plant. Prior to treatment, the water often goes through a pretreatment step in which larger debris that could potentially damage the treatment plant infrastructure is physically removed from the incoming water.
The drinking water treatment process involves a series of steps. Each step is designed to remove specific contaminants through physical and/or chemical mechanisms and is chosen based on the source water quality and available technology. Therefore, not all drinking water treatment plants apply the same treatment train.
However, several treatment strategies are the most commonly used, including coagulation and flocculation, sedimentation, filtration, and treatment with chemicals.
Once the water has been treated to meet the National Primary Drinking Water Standards, it is distributed to public utility customers, including households, businesses and schools, through a series of in-ground pipes. Secondary disinfection is added to limit bacterial growth as water moves through the distribution system. However, bacterial contamination is still possible, particularly as the infrastructure ages.