A March 1999, report by the National Academy of Sciences concluded that the current standard does not achieve EPA's goal of protecting public health and should be lowered as soon as possible. Under the Safe Drinking Water Act Amendments of 1996, EPA is required to publicize a final rule by January 1, 2001.

Long term exposure to low concentrations of arsenic in drinking water can lead to skin, bladder, lung, and prostate cancer. Non-cancer effects of ingesting arsenic at low levels include cardiovascular disease, diabetes, and anemia, as well as reproductive and developmental, immunological, and neurological effects.

Short-term exposure to high doses of arsenic can cause other adverse health effects, but such exposures do not occur from U.S. public water supplies at the current standard of 50 ppb. EPA set the current standard of 50 ppb in 1975, based on a Public Health Service standard originally established in 1942.

People at greatest risk from long-term exposure are children, pregnant and lactating women, and people with poor nutritional status and individuals with pre- existing diseases that affect specific organs.

For community water systems that require corrective action to meet a standard of 5 ppb, the EPA estimates that annual household costs will average $28 for Americans served by large systems and $85 for those served by small systems (those serving fewer than 10,000 people). Over 98 percent of the cost to a water utility will come from adding treatment equipment, chemicals, and management of the new treatment.

Since 1996, EPA's state revolving fund program has made available $3.6 billion to assist drinking water systems with projects to improve their infrastructure. EPA has funded over 1000 loans for projects around the country.

Arsenic occurs naturally in rocks and soil, water, air, and plants. It can be further released into the environment through natural activities such as volcanic action, erosion of rocks, and forest fires, or through human actions. Approximately 90 percent of industrial arsenic in the U.S. is used as a wood preservative, but arsenic is also used in paints, dyes, metals, drugs, soaps, and semi-conductors. Burning fossil fuels, paper production, cement manufacturing, and mining can also release arsenic into the environment.

While many community water systems may have no detected arsenic in their drinking water above 5 ppb, there may be "hot spots" with higher than the predicted levels of arsenic for that area. Water systems in western states that depend on underground sources of drinking water have naturally occurring levels of arsenic at levels greater than 10 ppb. Parts of the Midwest and New England have some systems whose current arsenic levels range from 2-10 ppb.

The EPA is also proposing a public health goal of zero for arsenic. The health goal is the level below which no known or anticipated health effects would occur. EPA sets public health goals at zero for all known carcinogens for which there is no dose considered safe.