Half of U.S. states have a high or very high prevalence of well water that's corrosive enough to leach lead from pipes.
That's the consensus of a new report from the U.S. Geological Survey that assessed groundwater of more than 20,000 private wells nationwide. About 44 million people in the U.S. get their drinking water from private wells.
"The corrosivity of untreated groundwater is only one of several factors that may affect the quality of household drinking water at the tap," Stephen Moulton, chief of the USGS National Water-Quality Program, said in a press release. "Nevertheless, it is an essential factor that should be carefully considered in testing for water quality in both public and private supplies nationwide."
Eleven states and the District of Columbia have a "very high prevalence" of potentially corrosive groundwater, a finding that could effect as many as 8 million people who depend upon self-supplied groundwater. To be designated "very high prevalence" the states scored high on both measurement indexes used in the study.
Fourteen states have a "high prevalence," meaning they scored high on one of the two gauges used in the study. About 16 million people live in states in this category and rely on self-supplied groundwater.
Nineteen states were seen as having a "moderate prevalence," and six states were classified as "low prevalence," according to the report.
The states with the largest percentage of wells with potentially corrosive groundwater are located primarily in the Northeast, the Southeast, and the Northwest. Virginia and Pennsylvania are states where private water sources, such as wells, springs, or cisterns, are especially common.
Kenneth Belitz, one of the researchers involved in the study, told CNBC they're only beginning to look at the factors that cause corrosivity. But geography and proximity to sources of chloride may be important factors.
"The rock and minerals affect chemical composition," he said. "The coastal plains on the East Coast tend to have more issues... The rainfall contributes chloride. Rain enters the ground and then it begins to move toward wells. As it moves through the system its chemical composition changes. The amount of time and the amount of rock that it has encountered will also affect the composition."
source: U.S. Geological Survey