An extensive new study confirms a long-suspected link between crippling birth defects and the nitrate contamination that threatens drinking water for 250,000 people in the San Joaquin Valley.

The study took place in the Midwest, but its findings hit hard in the Valley, where research last year showed farm-related nitrate pollution is extensive and expanding in the underground water of Fresno, Tulare and Kern counties.

The birth defects involved include spina bifida, cleft palate and missing limbs.

Valley clean-water advocates say the study again raises the profile of safe drinking water as a human right. Bureaucratic and funding delays have slowed fixes for years in many small towns.

“This contamination is so dangerous,” said Maria Herrera of the Visalia-based Community Water Center. “Many towns need help with their drinking water, and we’re still not seeing enough.”

The study from Texas A&M was published last month in the peer-reviewed journal Environmental Health Perspectives, making the strongest case to date about nitrates and birth defects.

Researchers looked at real-world situations, locating and contacting thousands of mothers using the National Birth Defects Prevention Study. Participants’ addresses were matched to drinking-water sources.

“We went beyond other studies to find out how much water pregnant women were drinking at home and at work,” said lead scientist Jean Brender, associate dean for research and a professor at the Texas A&M Health Science Center’s School of Rural Public Health.

The study focused on Iowa and Texas where nitrate problems are found in the groundwater. Nitrates can come from farm fertilizers and dairy waste. Other sources include septic systems, sewage treatment and decaying vegetation.

The study says mothers of babies with spina bifida were twice as likely to have consumed 5 milligrams or more of nitrate from their daily drinking water than women whose babies had no major defect.

Spina bifida is among several birth defects that happen during pregnancy as the baby’s brain and spinal cord develop. In some cases, spina bifida can result in bowel or bladder problems — in others, paralysis.

Many people living in rural Valley towns buy bottled water to protect themselves and their children from nitrates, which also can cause a potentially fatal blood disease in infants.

Many are forced to use 10% or more of their farmworker wages to pay for both bottled water and suspect tap water. When they cannot afford the bottled water, they drink from the tap, residents say.

Two years ago, the United Nations came to Seville, a town of 480 in Tulare County, as part of a worldwide tour of communities where drinking water is chronically unsafe. The U.N. investigator’s tour included communities in Costa Rica, Slovenia, Uruguay and Namibia.

The U.N. investigator recommended that California move with more urgency to address the problems, and the state has funded some projects. Money has been granted to study a solution in Seville.

The California Department of Public Health, which doles out money to improve rural water systems, last month announced a plan to push investment of $445 million of unspent federal drinking water funding. The report was ordered by the U.S. Environmental Protection Agency, which this year scolded the state for not spending the money.

Kathleen Billingsley, chief deputy director of policy and programs at the Department of Public Health, said, “The entire administration is committed to addressing the concerns outlined by the U.S. EPA.”

Back in Tulare County, some residents of small towns blame the water for unexplained stomach problems, hair loss and dizziness. Their biggest concerns are for pregnant women and infants.

“When I was taking care of my grandchild, I ran out of (bottled) water for the formula,” said Becky Quintana, a Seville resident. “I had to go buy more. I was not going to use the tap water.”

The nitrates problem is not just in Tulare County. A study released last year by the University of California at Davis showed the problem is widespread throughout Fresno and Kern counties in the Tulare Lake Basin, one of the most intensely farmed regions in the country.

Previous studies have suggested birth defects related to nitrate consumption, but the Texas A&M study went into more depth in looking at Iowa and Texas.

Researchers discovered about 25% of the participants in Iowa only drank bottled water, as did nearly half of them in Texas.

They compared birth defects among mothers who had very low exposures of nitrate from their drinking water to those who took in higher amounts of nitrate from water. Researchers took into account bottled water and tap water that either came from a municipal system or a private well.

The results might not be surprising. Researcher Brender said the women who drank water with low amounts of nitrates — bottled water, which was noted as having the least nitrate — were far less likely to have a child with birth defects.

Brender added that the research does not directly say nitrates cause the birth defects. There may be other chemicals, including pesticides, that have an impact. The researchers only examined nitrates in this study.

But she has advice for pregnant women and anyone else living in a rural area who drink water from a private well: “Get your private well tested, or drink bottled water.”