In March, as Mayor Eric Adams began an aggressive crackdown on New York City landlords who were behind on water bill payments, a public school safety agent and her family were presented with a brand-new $24,000 water bill.

If they did not pay at least $6,000 immediately, the city said, it would shut off the water to the home the woman shared with her husband, a diabetic car-service driver, and their 9- and 15-year-old children.

The mayor’s crackdown — announced in front of a boutique Manhattan hotel that was in arrears — suggested he was targeting large landlords, as a way to drum up payments to help preserve the vast water system on which all New Yorkers rely.

But the city may also be targeting homeowners who are aging, taking care of young children or suffering from serious medical problems, in defiance of state and city regulations that aim to protect vulnerable New Yorkers, according to a lawsuit filed Wednesday in Federal District Court in Brooklyn.

The crackdown by the city’s Department of Environmental Protection comes as it is struggling to fund its vast portfolio, a task made more difficult by the mayor’s diversion of more than $1.4 billion from the department to other city needs.

But the environmental agency’s demands are pressing: It must maintain the water and sewer systems, while also making the city less susceptible to flash flooding, a phenomenon that is growing more common with climate change. In 2021, flash flooding associated with Hurricane Ida drowned 11 New Yorkers in basements.