Issaquah’s city council must decide whether to include fluoride in its citywide water supply as part of an update to its water system plan.

About one-third of the city’s residents use water from the city’s wells, which pull from the Issaquah Valley aquifer. The water is non-fluoridated and serves residents in the Olde Town, Issaquah Valley and Squak Mountain neighborhoods. With the city’s population expected to grow from 37,000 to 50,000 by 2027, city officials say they need more water or the city will run out of new capacity by 2021.

Two-thirds of the city receives water purchased from the Cascade Water Alliance (CWA), which sources much of its water from Seattle Public Utilities, which fluoridates its water. Portions of North Issaquah are served by the Sammamish Plateau Water and Sewer District which also uses fluoride.

The additional water purchase was approved as part of the city’s water system plan adopted early this year. To facilitate this, the city will need to build a water treatment plant at a cost of roughly $28 million. The plant could treat the groundwater to match CWA water, including adding fluoride.

Issaquah public works engineering director Sheldon Lynne said this new blended water will be used to serve residents across the city. By bringing the well water to the same level of treatment as CWA water, the city can accurately tell residents exactly what’s in their water, including .7 parts-per-million (ppm) of fluoride.

If the city didn’t bring the water up to the same level of treatment, it would be mixing well water with CWA water, leading to an unknown level of fluoride in its drinking water. The city could choose to build a larger, more expensive plant which would filter out fluoride from the CWA supply too. That would increase the physical footprint of the treatment plant as well as require more funds for construction and maintenance.

Issaquah’s utilities engineering manager Robert York said at an Aug. 12 city council committee meeting that fluoridating and blending the city’s well water with CWA supply would increase the average water bill by about $.50. If the city were to remove it from the water it would raise bills by about $25.

“It would have a significant impact on rates,” York said.

Part of the cost increase stems from how the treatment plant options would work. If the city fluoridates its water, it will be added to the CWA supply outside of the plant. However, if fluoride is to be removed, the CWA water will need to be run through the plant.

Bill Osmunson is a Bellevue dentist, and of the residents who has opposed fluoridating the city’s water. He points to concerns about people receiving too much fluoride, which can cause a tooth decay disease called dental fluorosis.

“A little bit of fluoride, decay may go down a little bit — you get more fluoride and decay goes back up,” he said.

Osmunson said he’s worried that the .7 ppm may be too much when combined with other possible sources of fluoride people may be receiving, including in toothpaste. He would like the city to keep its well water non-fluoridated and instead suggested it let people choose whether they want fluoride.

“The city could provide it free, but they don’t have to medicate people against their will,” he said.

Water fluoridation has been standard practice in much of the U.S. for decades, with about 70 percent of people hooked up to public water systems drinking fluoridated water. Several deans from the University of Washington recently signed a letter supporting water fluoridation. Seattle Public Utilities has been fluoridating its water since the 1970s.

“Fluoridation has made an enormous impact on improving the oral health of the American people,” the letter read. “At the same time, we recognize that the public continues to receive periodic misinformation about fluoridation.”

The Issaquah City Council committee was thinking about those concerns at its Aug. 12 work session. The committee asked staff to bring in a public health expert to talk with the council about fluoride safety. The city council will need to decide whether to fluoridate its water within the next two months to keep the treatment plant project on track, staff said.