About 10 homes between Cornelius and Hillsboro experienced flooding recently after a water department employee — dispatched to make a chlorine-level adjustment on a city water line — made a misstep.

Tacy Steele, public information officer with the Hillsboro Water Department, said workers were checking on a water quality issue around 3 p.m. Tuesday, Nov. 19, when one accidentally turned the wrong valve, sending high-pressure water shooting through the city’s distribution system.

Several homeowners called the city to report leaking water heaters and oddly-running toilets, Steele said.

“Our worry was that this happened in the middle of the afternoon, and some homeowners would be at work,” said Steele, who added that city workers had the problem under control by 4 p.m.

The mishap affected about 110 homes along Tualatin Valley Highway between Northwest 334th and 341st avenues on the western edge of Hillsboro, Steele said, but fewer than a dozen flooded.

Cornelius City Manager Rob Drake said the homes — originally thought to be inside Cornelius city limits — were actually located in unincorporated Washington County. The water line servicing the homes originates in Cornelius near Coastal Farm and Ranch.

“They pull water in there off a 72-inch line that goes through Cornelius,” he said, describing it as gravity-fed water from the Washington County Joint Water Commission.

The transmission line serving the area is designed to handle 140 pounds of pressure, Steele noted, but water is typically run through a pressure-reducing valve to bring it down to 70 pounds. The water department employee mistakenly turned a bypass valve that had been installed during the 1990s, causing a sudden surge in pressure.

“The plan is to get that valve marked,” said Steele.

Homeowners in the affected area might have noticed rust-colored water coming from their pipes due to iron sediment loosened in the incident. Steele recommended that citizens flush their water, which she said is safe to drink. Residents were advised to run their faucets until the water turned clear.

Steele said homeowners who file claims with the city will be reimbursed by the water department, and that 10 claims had come in as of last Friday. Water department officials asked residents to check their water fixtures and hot water heaters for potential leaks.

Those who want to file a claim can contact Pat LeRoy, a senior property claims consultant with Citycounty Insurance Services in Lake Oswego, at 503-763-3872 or This email address is being protected from spambots. You need JavaScript enabled to view it.. After-hours staff at the Hillsboro Water Department can be reached at 503-615-6775.

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