Flint, Mich. — THE World Health Organization’s “action level” for lead contamination in drinking water — indicating the need for intervention — is 10 parts per billion. The Environmental Protection Agency’s action level is 15 parts per billion.

In tests of tap water in Flint., Mich., over the last six months, some 1,300 homes exceeded the E.P.A. action level. Thirty-two had levels above 1,000 parts per billion. And just this month, a sample showed a concentration as high as 11,846 parts per billion.

To understand the contamination of this city, think about drinking water through a straw coated in lead. As you sip, lead particles flake off into the water and are ingested. For almost two years, Flint’s children have been drinking water through lead-coated straws.

There are so many things wrong with this that it’s difficult to know what to address first. But since I called attention last year to an increase in children with elevated lead levels after the city changed its water supply, I’ve known that my focus had to be on the kids. One of my patients, a 2-year-old girl, recently came to the clinic for her checkup. Running around the room with her colorful gown flapping, she hopped onto the exam table, grabbed my stethoscope and placed it on her chest. I gently nudged it over her heart. “Can you hear anything?” Her eyes lit up, and she nodded.