Take the Drinking Water Quiz

The EPA requires all water suppliers to provide an annual report to their customers. This report, also called a consumer confidence report, includes information on the source of the water supplied and any contaminants found. You can contact your local water supplier for a copy of the report; the report also may be available online. There are more than 170,000 public water systems in the United States.

Bromate and chlorite are known as disinfection byproducts; they form when disinfectants added to drinking water combine with organic material in the water. Giardia is a parasite that contaminates drinking water through sewage and animal waste. Nitrates are nitrogen-containing substances commonly found in fertilizers. The EPA tracks more than 80 contaminants that may be found in drinking water. No water, not even water pumped from underground, is naturally pure. As water seeps through the ground to the aquifer, it dissolves and absorbs substances it comes in contact with. Some of these substances, such as minerals, are harmless, but other impurities can be harmful.

Turbidity, one indicator of water quality, is caused by the presence of tiny particles. The higher the turbidity, the greater is the likelihood that disease-causing microorganisms are present. High levels of turbidity may interfere with proper water treatment and monitoring.

Large metropolitan areas have water systems that draw from surface water, such as lakes, rivers, and streams. Smaller water systems use groundwater as their source. About 10 to 20 percent of people nationally use private wells for drinking water.

Most water suppliers add chlorine or another disinfectant to kill bacteria and other microorganisms, according to the EPA. Other methods of treatment depend on the source of the water. Water that is taken from a river or lake usually contains dirt, leaves, and other plant material, as well as certain contaminants. A water supplier often adds chemicals called coagulants to the water, which makes the dirt and contaminants form clumps and settle out of the water. The water then usually passes through a filter to remove any remaining solid particles, and is chlorinated to kill microorganisms. Water suppliers that draw water from the ground may not need to use coagulants and filters if the water is pure enough.

Young children are more vulnerable than adults to the effects of lead and nitrate. If you have lead pipes in your home, the EPA recommends that you use the cold water tap for making baby formula, drinking, and cooking. Let the water run for a minute or more if you haven't used the tap in at least six hours. If your water supply contains nitrates and your child is younger than 6 months of age, talk to your health care provider about whether you should find an alternative water source.

Bottled water isn't necessarily safer than tap water, according to the EPA. Both bottled water and tap water are safe to drink if they meet the standards set by the EPA and the Food and Drug Administration (FDA). Some bottled water is treated more rigorously than tap water, and some is treated less or not at all. Bottled water that contains sparkling water, seltzer water, tonic water, or club soda is considered a soft drink, and not regulated under FDA regulations for bottled water. Mineral water comes from an underground source and contains at least 250 parts per million (ppm) of dissolved minerals. Spring water comes from underground water that flows to the earth's surface; it can only be collected at the spring. Artesian water comes from underground water that is under pressure; that pressure pushes the water to the surface after a well is drilled.

Most people do not need to install a home water treatment system, according to the EPA. But if your water is unpleasant to drink, treating it can improve the taste. If you have young children at home or someone with a weakened immune system, treating the water yourself can help ensure that potentially harmful contaminants have been removed. Read up on the available products before you buy one, and decide what the purpose of the home treatment will be: Do you need better tasting water? Do you need extra protection against contaminants? No single treatment system can remove all contaminants.