Concern over the potential effects of long-term, chronic exposure to arsenic in drinking water has prompted the U.S. Environmental Protection Agency (EPA) to reduce the drinking water standard for arsenic from 50 parts per billion (ppb) to 10 ppb, effective January 26, 2006. Arsenic has been reported to cause more than 30 different adverse health effects including cardiovascular disease, diabetes mellitus, skin changes, nervous system damage, and various forms of cancer.The new standard will apply to most public drinking water systems in Idaho.

Arsenic has been reported to cause more than 30 different adverse health effects including cardiovascular disease, diabetes mellitus, skin changes, nervous system damage, and various forms of cancer.

Several factors working together will determine how likely it is for harmful health effects to occur. These factors are:

• Dose - how much arsenic you have been exposed to;
• Duration (exposure) - how long and how often you have been exposed; and
• General Health, Nutrition, Age and Lifestyle - some people may be affected by lower levels of arsenic in water than others. Young children, the elderly, people with certain long-term illnesses, people with poor nutrition, and people who smoke may be at greater risk.

EPA's proposed drinking water regulation addresses the long-term, chronic effects of exposure to low concentrations of inorganic arsenic in drinking water. Chronic effects at low concentrations include:

• Cancer effects: skin, bladder, lung, and prostate cancer.
• Non-cancer effects: skin pigmentation and keratosis (callus-like skin growths seen earliest and most often), gastrointestinal, cardiovascular, hormonal (e.g., diabetes), hematological (e.g., anemia), pulmonary, neurological, immunological, and reproductive/developmental functions.

Short-term exposure to high doses of arsenic (over 100-200 ppb) can cause other adverse health effects, but such effects are unlikely to occur from U.S. public water supplies that are in compliance with the existing arsenic standard of 50 ppb.

Arsenic in drinking water, soil, air, and food does pose health risks. Although a very high dose (60,000 micrograms) of arsenic can be lethal, the amount of arsenic in drinking water is very small by comparison and any health effects are the result of prolonged exposure over a period of years. The more you are exposed to arsenic over time, the higher the risk becomes for experiencing health effects. Different people may have different responses to the same exposure to arsenic, so there is no way to know exactly what may happen in any given case. Reducing the amount of arsenic allowed in drinking water will lessen people's exposure and reduce risk of adverse health effects.

For more information on the health impacts of arsenic in drinking water, visit EPA's Web site on Drinking Water and Health: What you need to know.

Compared to the rest of the United States, western states have higher arsenic levels (levels greater than 10 ppb). Parts of the Midwest and New England have some areas where arsenic levels are greater than 10 ppb. While many areas may not have detected arsenic in their drinking water above 10 ppb, there may be geographic "hot spots” with higher levels of arsenic than in surrounding areas.

View U.S. map showing arsenic concentrations (pdf 517 kb, 1 page).

Yes, it is, in some places. Levels are different in different parts of the state. There are 2,067 regulated public drinking water systems serving 1,082,873 people in Idaho. Approximately 95% of the state's drinking water comes from ground water. Surface water, including streams, rivers, reservoirs, and springs, supplies the remaining 5%.

Data compiled by the Idaho Department of Water Resources (IDWR) show that concentrations of arsenic in ground water are highest in the southwestern counties of Elmore, Gem, Owyhee, and Washington; in Kootenai County in northern Idaho; and Jefferson County in eastern Idaho. Other counties have moderate or only trace amounts of arsenic in ground water samples.

View Idaho map showing arsenic concentrations (pdf 497 kb, 1 page).

Neither the geologic sources or the complex geochemical processes by which arsenic is transported, stored, and released to ground water are well understood at the present time. As a first step toward understanding where arsenic is stored in the hydrologic environment and how it is being mobilized in ground water, DEQ and the U.S. Geological Survey recently conducted an investigation to identify possible geologic sources and storage sites of arsenic in the hydrologic environment in southwestern Idaho. DEQ plans to use this information and the results of future studies to develop strategies to prevent or mitigate arsenic contamination of drinking water supplies.

View Geochemical and Descriptive Data for Sedimentary Aquifer Materials in Southwestern Idaho on USGS Web site.

As of July 1, 2002, all community water systems (those that serve at least 15 service connections or 25 people year-round in their primary residences) are required to include health information and arsenic concentrations in their annual drinking water consumer confidence report (CCR) to DEQ for water that exceeds half the new standard (5 ppb). These reports may be disseminated to water system users. If you do not have access to your system's CCR, you may wish to contact them.

If you have a private well, have your well water tested by a certified drinking water laboratory. You will need to inquire whether the lab can test for arsenic.

View list of certified drinking water labs in Idaho.