"Our standard advice to private well owners is to test water for anything of local concern," said Cliff Treyens, NGWA's director of public outreach. "Contamination threats can vary from locale to locale with some caused by human activity and others such as arsenic occurring naturally in the environment. A good place to check on local groundwater contamination threats is the county health department."

The study by the US Geological Survey and the CDC's National Center for Environmental Health shows areas potentially affected by arsenic levels greater than 10 parts per billion - the federally established ‘maximum contaminant level' at which regulated public water systems are required to take corrective action. Private well water quality, however, is not regulated by the government on an ongoing basis. Private well owners are responsible for testing their water and taking action to keep it safe.

The study's top 10 states for people at risk for harmful arsenic exposure based on the size of the at-risk population were Michigan, Ohio, Indiana, North Carolina, California, Maine, Texas, Pennsylvania, Minnesota and Wisconsin.

To help well owners address the issue of arsenic in well water, NGWA has developed educational tools on testing water and treatment if necessary available on WellOwner.org.