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California Environmental Health Tracking Program

850 Marina Bay Pkwy, P-3
Richmond, CA 94804

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Last Edited: 8/11/2010

What are Drinking Water Contaminants?

The water we drink may contain natural or man-made contaminants. These contaminants are a potential threat to human health. Currently, CEHTP presents summary statistics about community water systems within California. At this time, data do not exist to tell us if individuals are actually being exposed to these contaminants or if contamination has resulted in adverse health effects. Learn more about drinking water contaminants and water quality below:

For information about water quality in California, view Drinking Water Quality Data.


Why are we concerned about water quality?

On average, each person consumes over two liters of water each day. As a result, drinking water may be a route of exposure to potentially hazardous substances. The presence of contaminants in water can lead to possible adverse immediate or long-term health effects, including gastrointestinal illness, reproductive problems, cancer, and neurological disorders.

For example, chlorine, in addition to killing or inactivating bacteria and other pathogens in water, can react with natural organic matter to produce potentially harmful byproducts. Water disinfection byproducts, arsenic, nitrate, and lead – all recognized water contaminants – can have important health effects in children, adults, and the unborn. US Environmental Protection Agency (EPA) sets maximum concentration levels for the chlorine byproducts as well as many other water chemicals and pollutants.

The majority of community water systems meet all health-based water quality standards. As a result, the risk of developing a disease from drinking water supplied by a community water system is low. At the same time, there are many diseases that might result from exposure to contaminants in drinking water.

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What are risks from drinking water contaminants?

The risk of developing a specific disease depends on many factors: the specific contaminant, the level and potency of that contaminant, the way the contaminant enters the body (for example, drinking or showering), and the person’s individual susceptibility. Sensitive people such as the elderly, children, and pregnant women are more likely to suffer ill effects than the rest of the population.

The specific health risks associated with the three contaminants presented on this website (arsenic, disinfection byproducts, and nitrate) are discussed in detail in the section for that contaminant.

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Keeping our water safe

The primary means of preventing health problems due to contaminants in drinking water is to ensure that drinking water meets or exceeds public health standards. Protecting water sources, providing effective and reliable water treatment, and monitoring water quality are the main strategies for providing high quality drinking water. Federal laws and regulations are in place at the state level to implement these strategies for community water systems.

The EPA regulates drinking water quality in public water systems. The United States has one of the most reliable systems of public water supplies, delivering generally high quality water to hundreds of millions of citizens. While the infrastructure and regulations help to assure the quality of this water, there are still areas where existing contaminant levels may pose some risks to the population.

There is a much lower level of assurance for those consumers served by small community water supplies not covered by the Safe Drinking Water Act (SDWA), or by private domestic wells which are virtually unregulated. As such, tracking hazards and exposures related to contaminants in drinking water remains an important aspect of an environmental public health tracking efforts at the state and national level.

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Who is testing your drinking water?

Water systems are required to serve drinking water that meets all drinking water standards.  They must conduct routine sampling and analysis of their drinking water supplies to certify compliance with Federal and State standards. 

Community Water Systems

A Community Water System (CWS) is a public water system that serves year-round residents of a community, subdivision, or mobile home park that has at least 15 service connections or an average of at least 25 residents. If you receive your drinking water from a CWS, you will receive a yearly “Consumer Confidence Report’ which contains information about the quality of water. It includes information on where the water comes from, how it is treated, a list of the chemicals they test for, and the highest concentration of each chemical that they found in the past year. If you did not receive a Consumer Confidence Report, you can obtain one by contacting your water supplier.

When a water system has a problem that might pose a risk to public health, the management is required to notify their customers. The most common problems are contaminant levels which exceed health standards (water quality violation) or problems with the water treatment system (treatment technique violation). If it is a serious situation, they must notify the public within 24 hours; for less serious problems they must notify the public within 30 days. In some circumstances water systems must work with the state drinking water program to prevent a more serious problem, even if there has not been a violation.

For more information on public notifications of drinking water problems, see EPA's public notification rule. If your public water system has notified you that there has been a problem, you should carefully follow the advice given by the water system and the local public health officials. If you think there is a problem with your drinking water, you should call your water provider. For help in locating these agencies or for information on drinking water in general, call EPA’s Safe Drinking Water Hotline: (800) 426-4791.

Private Domestic Wells

If you receive your drinking water from a private source, such as your own well, then it likely is not being tested for drinking water contaminants. If you have your own household water supply, you are responsible for maintaining and testing it.  Contact your local health department to find out if there are contaminants of concern in your area.

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