In urban areas, like Philadelphia, non point pollution is also caused by pollutants like oil and chemicals that enter the water systems during rain storms. Non point pollutants cloud the water, reduce oxygen supply, and disrupt stream habitat. In order for humans to use and consume water, water needs to be tested in water treatment facilities. The principal reasons for treatment are to reduce particulate matter, lower health risks with associated microbiological contaminants and improve color and taste characteristics. Typical water treatment processes include disinfection, filtration, flocculation, and sedimentation.
Disinfection protects against infectious disease by reducing the number of pathogens in the water.
However, disinfection can also introduces a small potential health risk due to the addition of chlorine. The chemicals used in these processes are typically of low toxicity and used at low concentrations. Inorganics added in water treatnent do not appear to pose a threat to public health either. Treated water is then used for a wide variety residential of uses that can be seen by figure 13. Water is also used in many commercial and industrial applications, and from the literature it is difficult to estimate the amount of water used in each application.