If you eat food in the U.S., you almost certainly eat fruits and vegetables grown in California’s San Joaquin Valley, a productive agricultural region also responsible for huge amounts of cotton. All Americans are connected to this part of the country and benefit in some way from the intensive farming that takes place there.

For people who live in the valley, agriculture is a vital part of their economic livelihood. But it is endangering another resource essential to life: Their drinking water.

According to a new study from the Pacific Institute, not only is the valley’s groundwater severely contaminated by nitrates from agricultural runoff, but clean drinking water is also unaffordable for as much as 40 percent of people who live in the Tulare Lake Basin. This region, in the southern part of the San Joaquin, mostly consists of rural communities as well as the cities of Fresno, Bakersfield and Visalia.

The report found that nearly 4,000 households in the study region spend at least 2 percent of their income for water services, and more than 7,000 households exceed this 2 percent threshold if you include what they pay for bottled water or purification systems — purchased because water from the tap is simply unsafe to drink.

That 2 percent number is significant because just last year, California passed legislation recognizing the “human right to water,” affirming, “every human being has the right to safe, affordable, and accessible water adequate for human consumption, cooking, and sanitary purposes.” The law uses 2 percent of median household income in a community as the benchmark of affordability.

But in some parts of the state, the report argues, that median household income figure fails to account for the poor. “Examining water affordability at the median household income only ensures that households at, or above, the median income have access to affordable water,” the authors write. “Using the standard approach to measuring affordability, we overlook the reality of households with income below the median.”

The problem is only getting worse. Water systems around the region are dealing with the gradual infiltration of generations of agricultural runoff — and not only nitrates, but also arsenic and other contaminants.

“As water quality worsens, water treatment costs will increase, and systems may be forced to increase their water rates,” according to the new report. “Unfortunately, this will likely lead to scenarios of increasing water bills in an area already plagued with high levels of unaffordability.”

For decades, the people of the San Joaquin Valley have absorbed the environmental effects of a hugely productive agricultural system that contaminates their drinking water with chemicals. (Nitrates in drinking water can actually be fatal to infants.) They also have struggled with entrenched poverty: Kern County, home to Bakersfield, recently ranked number one in the nation for food insecurity, and the city of Fresno ranked fifth.

If the water affordability legislation is to live up to its promise, researchers say, legislators and bureaucrats will have to carefully consider how they determine what people can reasonably pay.

“[A]gencies charged with implementing a human right to water should consider using a measure that correctly assesses those members of the population who are most vulnerable,” the researchers write. “Rural areas of California like the [Tulare Lake Basin] represent a major challenge to ensuring the state’s commitment to a human right to water.”

Sarah Goodyear has written about cities for a variety of publications, including CityLab, Grist and Streetsblog. She lives in Brooklyn.

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