Like Ms. Serrato, the vast majority of residents here in the Sierra Nevada foothills are Mexican immigrants, drawn to the state’s Central Valley to work in the expansive agricultural fields. Many here have spent lifetimes scraping together money to buy their own small slice of land, often with a mobile home sitting on top. Hundreds of these homes are hooked to wells that are treated as private property: When the water is there, it is solely controlled by owners. Because the land is unincorporated, it is not part of a municipal water system, and connecting to one would be prohibitively expensive.

The Gallegos family’s drinking water comes only from bottles, mostly received through donations but sometimes bought at the gas station. For bathing, doing dishes and flushing toilets, the family relies on buckets filled with water from a tank set in the front lawn, which Mr. Gallegos replenishes every other day at the county fire station. Often, the water runs out before he returns home from his job as a mechanic, forcing Ms. Gallegos to wait for hours before she can clean.

The family has spent hundreds of dollars to wash their clothes at the laundromat and on paper goods to avoid washing dishes. Ms. Gallegos recently told her 10-year-old daughter that there was no money left to pay for her after-school cheerleading club.