The EPA set the current standard of 50 ppb in 1975 based on a Public Health Service Standard originally set in 1942. In March 1999, the National Academy of Sciences (NAS) completed a review of updated scientific data on arsenic and recommended that EPA lower the standard as soon as possible. Although the NAS did not recommend a specific numeric level, its recommendation formed the basis for EPA's proposal today.
All 54,000 community water systems, serving 254 million people would be subject to the new standard. However, EPA estimates that only 12 percent of community water systems, approximately 6,600, would need to take corrective actions to lower arsenic levels in drinking water to 5 ppb. Ninety-four percent of these water systems serve fewer than 10,000 people each.
Arsenic can contaminate drinking water through natural processes, such as erosion of rocks and minerals. Arsenic can also contaminate drinking water when used for industrial purposes. Arsenic is found at higher levels in underground sources of drinking water than in surface waters such as lakes, reservoirs, and rivers.
Water systems in western states and parts of the Midwest and New England that depend on underground sources of drinking water will be most affected by this proposal.
For those systems that need to take corrective action to comply with the proposed standard, EPA estimates annual household costs to average $28 for Americans served by large systems and $85 for those served by systems serving fewer than 10,000 people.
(Source: U.S. Environmental Protection Agency)
