The safety of California's groundwater, which is the largest source of drinking water, is managed through the state's Clean Water Act. But each source of contamination is handled differently and agriculture is more lightly regulated than other industries.

Problem to Worsen by 2050

Nitrate contamination in groundwater from fertilizer and animal manure is severe and getting worse for hundreds of thousands of residents in California’s farming communities, according to a study released by researchers at UC Davis.

Nearly 10 percent of the 2.6 million people living in the Tulare Lake Basin and Salinas Valley might be drinking nitrate-contaminated water, researchers found. If nothing is done to stem the problem, the report warns, those at risk for health and financial problems may number nearly 80 percent by 2050.

The report is the most comprehensive assessment so far of nitrate contamination in California’s agricultural areas.

High nitrate levels in drinking water are known to cause skin rashes, hair loss, birth defects and “blue baby syndrome,” a potentially fatal blood disorder in infants. A recent National Institutes of Health study linked increased risk of thyroid cancer with high nitrate levels in public water supplies.

Nitrate-contaminated water is a well-documented fact in many of California’s farming communities. The agricultural industry, however, has maintained that it is not solely responsible because nitrates come from many sources.

But according to the UC Davis report, 96 percent of nitrate contamination comes from agriculture, while only 4 percent can be traced to water treatment plants, septic systems, food processing, landscaping and other sources.

In addition to health risks, tainted water will exact a growing financial toll, the report said. The researchers project that utilities and citizens in the two regions will pay $20 million to $36 million per year for water treatment and alternative supplies.

According to the study, more than 1.3 million people in the two areas currently face increased costs as residents seek alternative sources of water and providers pass on the costs of treatment to ratepayers.

The five counties in the study area – among the top 10 agricultural producing counties in the United States – include about 40 percent of California’s irrigated cropland and more than half of its dairy herds, representing a $13.7 billion slice of the state’s economy.

The Central Coast Regional Water Quality Control Board has produced several reports of its own that show “large-scale degradation” of drinking water aquifers due to nitrates from fertilizer.

Nitrates are odorless, tasteless compounds that form when nitrogen from ammonia and other sources mix with water. While nitrogen and nitrates occur naturally, the advent of synthetic fertilizer has coincided with a dramatic increase in nitrates in drinking water.

Large portions of this article first appeared on msnbc.com. For more in-depth information, please read “Farming communities facing crisis over nitrate pollution, study says” by Stett Holbrook, from the Food & Environment Reporting Network.