CHE logo

Washington StateThe Collaborative on Health and the Environment – Washington

A Partnership Network for Environmental Health
Established and Coordinated by the Institute for Children's Environmental Health

physician and child Seattle Space Needle and monorail smokestacks a child with her grandmother child on a playground girl at a drinking fountain orca Mt. Rainier over Tacoma


This section of the clearinghouse contains information on chemical contaminants in drinking water. Drinking water can also contain micro-organisms harmful to health. As well, exposure to chemical contaminants in surface waters, such as lakes and rivers, can result in exposure to chemical contaminants.

Access to a supply of clean, safe drinking water is essential for human life. Without water, human life cannot be sustained for more than about three days. Yet at the same time, chemical contaminants in drinking water have been linked with a variety of different types of diseases and disabilities, including cancer and birth defects.

Many chemical contaminants including heavy metals, such as lead and cadmium, pesticides, and other types of organic chemicals have been detected in drinking water. Some of the greatest concerns are associated with the presence of chlorination by-products in chlorinated drinking water. Chlorine and related chemicals are often added to ‘raw’ water during the treatment process, especially to surface water from lakes and rivers. These chemicals react with naturally occurring substances to form chlorination by-products, such as trihalomethanes and haloacetic acids. These substances can have effects on health, for example, some of the trihalomethanes are known to cause cancer.

Summary of Washington State Data

From National Organizations:

Annual drinking water quality consumer reports on each of 17 public water systems in Washington State are available from the US Environmental Protection Agency. These reports are quite general and contain information on levels of trihalomethanes, haloacetic acids, lead and a few other contaminants.

A 2003 national study called "What's on Tap?" conducted by the Natural Resources Defense Council included the City of Seattle. It found that Seattle's watershed controls were among the best in the country, however, in 1997/98 14% of the homes tested exceeded the national action level for lead of 15 parts per billion.

In December 2005, the Environmental Working Group released its "National Assessment of Tap Water Quality". This study includes information on tap water quality in Washington, showing that a total of 84 contaminants were detected on one or more occasion between 1998-2002, including agricultural pollutants, sprawl and urban pollutants, industrial pollutants, water treatment and distribution by-products, naturally occurring substances, and unregulated compounds.

Two related studies have examined levels of "Pesticides in Public Supply Wells of Washington State". One State-wide study found that pesticides were detected in 6% of the wells tested and that 21 of the 27 pesticides analysed for, were detected. Frequently detected pesticides included atrazine, simazine, dicamba, 2,4,5-TP, 2,4-DB, picloram and metribuzin. The second study had lower detection levels and was conducted by the US Geological Survey (USGS). It found pesticides in 30% of the wells tested. Frequently detected pesticides included atrazine, simazine, prometon, DDE, tebuthiuron and metribuzin.

In 2006, the US Geological Service (USGS) has published a report on "Pesticides in the Nation's Streams and Groundwater", including general information on Washington State. A total of 27 individual factsheets are available, containing detailed information on pesticides and other contaminants in water.

The USGS has also developed a National Water Quality Assessment Data Warehouse that contains data on levels of pesticides and other contaminants in samples of surface water and groundwater.

From State Organizations:

The Washington State Department of Health's "Drinking Water Program Overview" states that "More than 5 million of Washington State's nearly 5.9 million people are served by 16,717 public water systems. Of these 16,717 public water systems, the vast majority -14,888 - is privately owned".

The Department of Health website does not provide much information on contaminants in drinking water in Washington State. It does produce an annual report on trends among its drinking water systems, called "Enforcing Drinking Water Regulations".

In 2004-2005, the Office of the Superintendent of Public Instruction (OSPI) and the Department of Health (DOH) jointly implemented a "School Lead Testing Grant Program" to partially reimburse Washington public elementary schools for the cost of initial testing for lead in their drinking water. Of 7,728 samples collected, 559 or 7.2 percent were at or above 20 parts per billion (ppb) for lead. The U.S. Environmental Protection Agency recommends action when the lead concentration at a specific outlet within a school is more than 20 parts per billion.

The Department of Ecology used to monitor levels of pesticides in surface waters in Washington State. The last report was published in 2000 and summarized data from 1997. The report is called "Washington State Pesticide Monitoring Program: 1997 Surface Water Sampling Report".

From Local Organizations:

The results of water tests at Seattle public schools are available.


Information on Washington State in Context

According to the Environmental Working Group study "A National Assessment of Tap Water Quality", Washington State's drinking water quality is the 17th worst of the 42 States studied, as judged by the number of contaminants detected, the number of contaminants over health limits, the total population exposed, and the population exposed over the health limits.

Quality of Information on Washington State

Information on drinking water quality in Washington State is good. Consumers are provided with an annual Consumer Confidence Report, summarizing drinking water quality for their supply. However, there is a need for a publicly accessible, queryable State-wide database, with mapping capacity. Also, there is a need for studies on chemicals in drinking water and health outcomes, such as those that have been observed in studies conducted elsewhere in the US and Canada.


General Information Sources

Environmental Protection Agency:

Natural Resources Defense Council:

Environmental Working Group:

Washington State Department of Health:

US Geological Survey: