WHEN MY YOUNG daughter says she’s thirsty, I take for granted that the water from our kitchen tap is clean and safe. In fact, that’s what most Americans assume. But should we?

As we mark World Water Day on March 22, the disturbing truth is that roughly a quarter of Americans drink from water systems that violate the Safe Drinking Water Act. Violations range from failing to properly test water to allowing dangerous levels of lead or arsenic—and occur everywhere: in rural communities and big cities, in red states and blue ones.

The lead contamination crisis in Flint, Michigan, was extreme—and shocking because of the role that race played. However, it was not an isolated case, and we need to consider it a national wake-up call.