Public drinking water is obtained from surface water, which may be found in rivers, lakes and reservoirs. It is easily contaminated due to acid rain, highway runoff, pesticides, dumping of industrial wastes, as well as human and animal wastes. This contamination can be reversed with fresh rain, aeration, sunlight and certain plants and microorganisms found in the water.

Public drinking water is disinfected and treated to remove detected contaminants when they exceed acceptable levels established by the Environmental Protection Agency (EPA). The most common disinfection method is the addition of chlorine to the water supply. Chlorine kills fecal bacteria that may cause life-threatening waterborne diseases (e.g., cholera, dysentery, typhoid fever). These are no longer a public health threat in the United States due to chlorine disinfection. Another disinfectant method is the use of ultraviolet light to kill harmful microorganisms.

Municipal water suppliers provide an annual water quality report called the Consumer Confidence Report. It includes the following information:

• Quality of the drinking water in the past calendar year
• Source of the water
• Levels and suspected sources of contaminants
• Maximum contaminant levels
• Treatments used

Well water (groundwater) is found in aquifers and pumped to the surface. Contamination is difficult, but can occur due to seepage from hazardous waste sites, landfills, dumps, underground gasoline and chemical tanks, or improperly disposed of household chemicals and solvents. Well water does not receive the benefit of the sun, air or aerobic organisms that may help neutralize certain types of water contamination. Well owners are advised to annually test the quality of their water.

According to the EPA, approximately 15 percent of people in the United States use private drinking water wells. The EPA does not regulate the quality of water from these sources, but most state and local governments have laws that govern the safety of water from private wells.