Millions of tons of nitrate from industrial farming find their way into America’s drinking water each year, causing thousands of cases of cancer and other health problems, an environmental advocacy group says.

In a new report, researchers from the Environmental Working Group (EWG) quantify the risk. They say nitrate is responsible for nearly 12,600 cases of cancer a year.

“Industrialized farming relies heavily on nitrate fertilizers that can run off into the water table used by drinking water utilities,” said Sydney Evans, a science analyst at EWG.

The risk varies from region to region, she said, noting that many small farming communities have the highest nitrate levels in their water — and the highest risk. Iowa and California, two heavily agricultural states, were found to have the most nitrate-related cancer cases.

A Yale University researcher who reviewed the report said the danger it highlights is clear and exists throughout the country.

“An immediate response is warranted, so that we are not poisoning our water to produce our food,” said Dr. David Katz, director of the Yale-Griffin Prevention Research Center in New Haven, Conn.

The report said 80% of the nitrate-related cancers were colorectal, with ovarian, thyroid, kidney and bladder cancer accounting for the rest. Treatment costs up to $1.5 billion a year, according to the report.

Nitrate in tap water also has been tied to serious health issues for infants, the researchers said. Among them: nearly 3,000 babies with very low birth weight; more than 1,700 preterm births; and 41 cases of neural tube defects each year in the United States.

Katz said that although the study has limitations, it makes a compelling case that nitrates from what he described as “agriculture as usual” in the United States are “imposing grave costs measured in both lives and dollars.”

Meanwhile, Evans called on the U.S. Environmental Protection Agency (EPA) to revisit its public health standards for drinking water. A main mission of her group is to prevent nitrate from fouling drinking water.

Since 1962, the federal standard for nitrate in drinking water has stood at 10 milligrams per liter. The report said problems have been found at one-tenth of that level.

The EPA was slated to re-evaluate its standards with an eye to reducing the permissible level in drinking water, but the Trump administration canceled those plans, Evans said.

For tap water to be safe, she said, nitrate levels would have to be 70 times lower than today.

Nitrate is hard and costly to filter out of water, Evans said. Some towns and cities, however, do remove it and pass along the cost to residents.

Private wells can also have high nitrate levels. People who rely on well water have to spend thousands of dollars to add reverse osmosis systems if they want to remove nitrate, Evans said.