Many people choose to buy bottled water instead of drinking tap water from their local water systems. Others purchase filter systems such as the Brita water pitcher, hoping to remove dangerous chemicals. Water is necessary for life, but today the water we drink often contains substances that are not only unnecessary for life, but even harmful. Chemicals in water supplies can cause many health problems, particularly cancer.

Water from the ground – wells or springs – is generally considered safer than surface water from lakes or rivers. However, research has shown that, due to seepage from landfills and toxic waste disposal sites, well or spring water can be dangerous too. Here is what you need to know about this problem:

Volatile organic compounds (VOCs) are chemicals containing carbon that evaporate easily. Some of them degrade quickly, but others stay in the environment for decades. These chemicals are found in many common products including cleaners, deodorizers, paints, adhesives, and refrigerants. Once used, VOCs may remain in the atmosphere or move to soil, surface water, or ground water. Many VOCs are known carcinogens or may seriously affect human health, according to the Environmental Protection Agency (EPA).

In one study, over 65% of the wells sampled contained one or more VOCs. Chloroform, toluene, trimethylbenzene, and percholoroethene were detected in more than 10% of the samples. Other VOCs occurred less frequently; mixtures were commonly reported (31%). Overall, the VOC concentrations were lower than levels considered to be dangerous to humans. However, according to the National Resources Defense Council, the lower levels can still have adverse effects for pregnant or nursing women, the elderly, individuals with HIV/AIDS or otherwise compromised immune systems, and those with chronic illnesses.

Lead is another potential water contaminant. It may result from old or damaged pipes in the plumbing of your home. The presence of lead in city water, regardless of its source, may also be increased by the use of chloramines as disinfectants (reported in Environmental Health Perspectives). Lead poisoning can occur suddenly, with convulsions, paralysis, or vomiting and diarrhea, or over time, as lead slowly accumulates in the person’s body. This is especially dangerous for children since lead interferes with neurological development.

A lesser known problem is sewage overflow. This can occur during heavy rains, when a pipe breaks, or when a pump malfunctions. Depending on the type of sewage system, the overflow may be diluted or undiluted and may enter ground water, surface waterways, streets, or other areas including playgrounds. Untreated sewage can cause many illnesses, particularly hepatitis and gastroenteritis. Unfortunately, the public is not always notified when a sewage overflow occurs.

Knowledge is your best ally. Contact your local water treatment authority or the EPA for information about the treatment plants in your area. If your water comes from a private well, have the water tested for VOCs, heavy metals, and other contaminants. Although the government is charged with protecting our resources and health, we also must be responsible and pro-active!