New Drinking Water Standard for Arsenic

The Environmental Protection Agency (EPA) has finalized a regulation to reduce the public health risks from arsenic in drinking water. The Agency is revising the current drinking water standard for arsenic from 50 parts per billion (ppb) to 10 ppb. This revision will provide additional protection for 13 million Americans against cancer and other health problems, including cardiovascular disease and diabetes, as well as neurological effects.


Studies have linked long-term exposure to arsenic in drinking water to cancer of the bladder, lungs, skin, kidney, nasal passages, liver, and prostate. Non-cancer effects of ingesting arsenic include cardiovascular, pulmonary, immunological, neurological, and endocrine (e.g., diabetes) effects.

Short-term exposure to high doses of arsenic 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.

The current standard of 50 ppb was set by EPA in 1975, based on a Public Health Service standard originally established in 1942. 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.

On June 22, 2000, EPA proposed a new drinking water standard of 5 ppb for arsenic and requested comment on options of 3 ppb, 10 ppb, and 20 ppb. EPA evaluated over 6,500 pages of comments from 1,100 responses. Under the Safe Drinking Water Act Amendments of 1996, EPA was required to issue a final rule by January 1, 2001 and Congress subsequently extended this date to June 22, 2001.  On January 22, 2001 the official version of the final rule was published in the Federal Register. The final rule can be found on the Internet at

The Safe Drinking Water Act, as amended in 1996, requires EPA to revise the existing drinking water standard for arsenic. The new standard will protect against possible adverse health effects from exposure to this contaminant and will reflect the statutory evaluation of whether the costs are justified by the benefits. The process for revising the standard is complex, and EPA must consider a range of scientific, economic, and programmatic factors.

Final Rule

In 1996, Congress established certain requirements EPA must meet in designating a new standard for arsenic. These requirements have shaped the agency's strategic approach. EPA will use peer-reviewed health effects research to meet the statutory deadlines, along with studies of treatment, analytical methods, occurrence, and cost-benefits, and will identify affordable small system technologies. Results of focused long-term arsenic research efforts will be considered in future reviews of the Maximum Contamination Level (MCL), which will be evaluated at least every six years, as appropriate, as required by the 1996 amendments.

The Safe Drinking Water Act requires EPA to set the MCL as close to a public health goal as feasible, taking into consideration treatment technology and regulatory costs and benefits. For the new standard, EPA must identify affordable small system technologies.

Currently, the arsenic MCL only applies to community water supplies, such as those supplying houses, apartments, mobile home parks, and condominiums. The new MCL would also apply to non-transient non-community systems, such as those supplying schools and office buildings.

The new standard will apply to all 54,000 community water systems. A community water system is a system that serves 15 locations or 25 residents year-round, including most cities and towns, apartments, and mobile home parks with their own water supplies. EPA estimates that roughly five percent, or 3,000, of community water systems, serving 11 million people, will have to take corrective action to lower the current levels of arsenic in their drinking water.

The new standard will also apply to 20,000 water systems that serve at least 25 of the same people more than six months of the year, such as schools, churches, nursing homes, and factories. EPA estimates that five percent, or 1,100, of these water systems, serving approximately 2 million people, will need to take measures to meet the new arsenic standard. Of all of the affected systems, 97 percent are small systems that serve fewer than 10,000 people each.

Arsenic Occurrence

Arsenic occurs naturally in rocks and soil, water, air, and plants and animals. 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 currently used as a wood preservative, but arsenic is also used in paints, dyes, metals, drugs, soaps, and semi-conductors. Agricultural applications, mining, and smelting also contribute to arsenic releases in the environment.

Higher levels of arsenic tend to be found more in ground water sources than in surface water sources (i.e., lakes and rivers) of drinking water. Compared to the rest of the United States, western states have more systems with arsenic levels greater than 10 ppb. Parts of the Midwest and New England have some systems whose current arsenic levels are greater than 10 ppb, but more systems with arsenic levels that range from 2-10 ppb.


The average increase in household cost for water that meets the new arsenic standards depends on the size of the water system and how many people are served by that system. For small community water systems (those serving fewer than 10,000 people), the increase in cost is expected to range between $38 and $327. For community water systems that serve greater than 10,000 people, annual household costs for water are expected to increase from $0.86 to $32.

Systems may apply for financial assistance through EPA's drinking water state revolving fund. Since 1996, EPA's drinking water 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. In addition to financial assistance, compliance period extensions of up to 9 years (resulting in a total compliance period of 14 years) are available to small systems through an exemption process.

How soon after publishing the final rule will the changes take effect?

All community water systems and all non-transient non-community systems that exceed the MCL of 10 micrograms per liter will be required to come into compliance five years after the publication of the final rule. Beginning with reports that are due by July 1, 2002, all community water systems will begin providing health information and arsenic concentrations in their annual consumer confidence report (CCR) for water that exceeds one-half the new MCL.