Whenever Jamison Rich got thirsty after gym or recess, he took a drink from the nearest water fountain at his elementary school.

Only last month did his family learn that the water bubbling out of some fountains contained high levels of lead, a notorious toxin that can silently damage developing brains and slow growth in little bodies like his.

Recently, a blood test on the 7-year-old found more than twice the average level of lead for young children, even though as far as anyone knows he's never come in contact with lead paint or tainted soil.

Jamison's school, Caroline Elementary in Ithaca, N.Y., is one of hundreds across the nation where children were exposed to water containing excessive amounts of an element doctors agree is unsafe at any level, a USA TODAY NETWORK investigation found. An analysis of U.S. Environmental Protection Agency data showed 353 schools and day-care centers failed lead tests a total of 471 times from 2012 through 2015.

That represents nearly 20% of the water systems nationally testing above the agency's "action level" of 15 parts per billion.

One water sample at a Maine elementary school was 41 times higher while another at a Pennsylvania preschool was 14 times higher. And a sink in a music-room bathroom at Caroline Elementary tested this year at 5,000 ppb of lead, results released by the school system show.

That's the cutoff where the EPA labels a substance “hazardous waste.”