TIGARD — Beaverton’s plan to fluoridate its drinking water is creating ripples in neighboring cities.

The Tigard City Council on Tuesday heard a presentation about how fluoridation may affect Tigard and the surrounding area.

Tigard is negotiating to receive up to 4 million gallons of drinking water a day from the Joint Water Commission, which delivers the water through Beaverton, said Dennis Koellermeier, Tigard’s assistant public works director.

The water would serve not only Tigard, but also King City, Durham and parts of unincorporated Washington County.

In November, Beaverton residents in an advisory vote approved fluoridating their water.

“This is a new wrinkle we did not anticipate a year ago,” Koellermeier said.

Beaverton expects to finish exploring a final technical issue in about a month. If all goes well, the city may begin fluoridating its water as early as January, Koellermeier said, which means Tigard customers could receive fluoride in their water.

The debate over fluoridation is nothing new. Fluoride in water has been proved to help prevent tooth decay. High concentrations of fluoride, however, can have adverse effects, including fluorosis, which leaves teeth stained or brittle, according to a report prepared for Tigard by engineering consultants Murray, Smith & Associates of Portland.

Cities across the United States have been adding fluoride to water since 1945, the report said.

According to figures from the Oregon Department of Human Services, about 629,000 Oregon residents receive fluoridated water. Districts providing fluoridated water include Forest Grove, Tualatin Valley Water District, Salem and Keizer.

Tualatin Valley Water District provides fluoridated water to all its customers except those in the Metzger area.

Hillsboro has explored fluoridating its water, but city officials decided earlier this year to put the discussion on hold.

Even with limited discussion Tuesday, Tigard staff and councilors have begun wading through a series of hard questions that may arise if Beaverton offers fluoridated water.

Water from Beaverton makes up about 20 percent to 40 percent of the daily supply for Tigard and surrounding areas, Koellermeier said.

Tigard also receives water from other sources, including Portland’s Bull Run system.

Because Tigard uses a mix of water, fluoride levels could vary depending on where a customer lives and the day of use.

Koellermeier raised the issue of whether the city had to provide a consistent level of fluoride to all customers all the time.

Mayor Jim Griffith asked whether the city should have an advisory vote on the issue, but city staff said Tigard could only hold an advisory vote within its city limits and would not be able to poll King City or Durham customers.

The engineering consultants’ report presented the City Council with three suggestions: accept the fluoridated water; cease using the water; or remove the fluoride from the water. The third option, however, was not a realistic option because of its cost and effectiveness, the report concluded.

The City Council is expected to revisit the issue in about a month.