Francisco Diaz remembers when the water piped to his home in the Central Valley community of Monterey Park Tract made everything smell rotten, including himself.

“We had to take our clothes and go to the city and wash it over there because if you had washed it here and put it on, you’d stink,” said Diaz, who heads the Monterey Park Tract Community Service District, a form of specialized local government. “We couldn’t even take showers.”

Unsurprisingly, the water was undrinkable. Agricultural run-off, heavy in potentially toxic nitrates, had contaminated both wells that supplied water to Monterey Park Tract, nestled amid the crop fields and dairy farms of Stanislaus County.