In 1974, Congress passed the Safe Drinking Water Act, which authorized the U.S. Environmental Protection Agency (USEPA) to set national drinking water standards. In addition, all public water systems must monitor drinking water quality and notify people about water system contamination.

All drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants.

As water travels over the surface of the land or through the ground, it can pick up substances resulting from the presence of animals or from human activity.

The presence of contaminants does not necessarily indicate that water poses a health risk. More information about contaminants and potential health effects can be obtained by calling the USEPA's Safe Drinking Water Hotline (1-800-426-4791).

Water must go though an extensive treatment process before it is considered safe to drink. Also, your drinking water is protected from unsafe levels of chemicals and bacteria by regularly scheduled testing. Drinking water wells are tested weekly, monthly, quarterly, annually or up to once every five years depending on the type of chemical, the vulnerability of the well to nearby potential sources of contamination and historic water quality information. Wells that may have the potential to be contaminated are tested more frequently. Testing intervals are set by the California Department of Health Services. Historically, California standards are more stringent than the federal counterparts.

Some people may be more vulnerable to contaminants in drinking water than the general population. Immunocompromised persons such as persons with cancer undergoing chemotherapy, persons who have undergone organ transplants, people with HIV/AIDS or other immune system disorders, some elderly and infants can be particularly at risk from infections. These people should seek advice about drinking water from their health care providers.

The Environmental Protection Agency/Centers for Disease Control guidelines on appropriate means to lessen the risk of infection of Cryptosporidium and other microbial contaminants are available from the federal EPA's Safe Drinking WaterHotline (1-800 426-4791).