SAN FRANCISCO » Half of U.S. states have a high prevalence of well water that’s corrosive enough to leach lead from pipes, the U.S. Geological Survey said today.

The findings were based on the broadest sampling yet of untreated groundwater from private wells supplying 44 million Americans, the federal agency said.

While federal and state governments regulate public water supplies, testing and treating water in private wells is almost entirely the responsibility of homeowners.

The study provides a reminder that routine testing of well water, including its likeliness to leach lead from plumbing, is essential for homeowners, said Stephen Moulton, chief of the USGS water quality program.

The study does not apply directly to the water crisis in Flint, Michigan, where treated river water drew dangerous levels of lead from pipes into drinking water.

The USGS sampled untreated groundwater in more than 20,000 wells nationwide.

Corrosive groundwater was rated very prevalent in Alabama, Connecticut, Delaware, Georgia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, Rhode Island and South Carolina, as well as the District of Columbia.

Another 14 states had a slighter but still high percentage of wells with corrosive groundwater. Those were generally Eastern states but included Washington, Oregon and Hawaii.