WASHINGTON (AP) _ The Environmental Protection Agency wants to reduce the limit for arsenic allowed in drinking water to one-tenth the current standard in an effort to reduce cancer risks.

The agency proposed on Wednesday to reduce the arsenic allowed in drinking water from 50 parts per billion to 5 parts per billion.

An estimated 6,600 water systems nationwide serving at least 22.5 million people would need to upgrade their systems to meet the standard.

Industry officials say the new standard could increase household water costs up to $100 a year for customers largely in the rural Southwest and pockets of New England where arsenic levels are highest.

The EPA is asking for public comments for 90 days about lowering the standard. After reviewing the comments, a final rule could be put in place by early 2001.

If a lower standard is set, large water systems serving 10,000 people or more would have three years to make improvements and smaller systems would have five years. About 95 percent of the systems failing to meet the proposed standard are small systems.

Water industry representatives, who agree that the current arsenic standard is too high, are pushing for a standard of 10 parts per billion, which would match the World Health Organization standard.

Efforts to reduce arsenic drinking water followed a National Academy of Sciences report in 1999 that found arsenic in drinking water causes bladder, lung and skin cancer, and might cause kidney and liver cancer.

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On the Net: U.S. Geological Survey map of counties with high arsenic levels: http://co.water.usgs.gov/trace/arsenic