PLEASANTON — Students at Alisal Elementary School and Amador Valley High School were warned not to drink the water Monday morning after a work crew accidentally released a high concentration of fluoride into the water system the night before.

City officials said the crew was working to replace a valve at the water pumping station on Santa Rita Road near Alisal Elementary on Sunday night.

Scott Baker, assistant director of public works/operations for Pleasanton, said a worker accidentally shut off a valve, causing 120 gallons of fluoride to flood the water supply.

Negative pressure created by the shutoff pulled the fluoride south toward the Jensen Tract area, Baker said. Water monitors became aware of the problem shortly after 6 a.m. Monday.

“Once we became aware of it, we started flushing the system and notifying people in the area not to drink the water,” Baker said.

Fire hydrants throughout the area were opened to flush the system clean, officials said.

“We’re very serious about the public’s safety and health,” Baker said. “When something like this happens, we’re very concerned.”

School officials said the Pleasanton Unified School District was notified and worked with the city to monitor the water supply at Alisal Elementary and Amador Valley High School.

“We were in immediate contact with the schools,” Baker said. “We advised them to flush their sites and take repeated tests.”

School officials said students were told not to drink the water until mid-morning Monday, when tests by city staff confirmed the fluoride content had dropped to a safe level.

Water is fluorinated to prevent cavities and other dental problems, Baker said. Too much fluoride, however, can result in fluoride poisoning, the symptoms of which are diarrhea, nausea and vomiting.

“It’s a real short order. The symptoms generally occur with- in the hour — or less,” Baker said. “We’re not aware of anyone reporting a case of fluoride sickness. We’re keeping our fingers crossed.”

Baker said tests confirmed the water was safe to drink early Monday afternoon.

“All the water in the mains are at acceptable fluoride levels,” he said. “Some people may still have some trapped in their water lines. We’re asking people to run the faucets they drink from for 10 to 15 minutes to clean them out.”

Baker said once the problem was detected, the city water department worked quickly to address it. “When it comes to the public’s health and safety, it’s our system and it’s our responsibility,” he said.

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