Few issues fire up Oregonians quite like the debate over fluoride in the public water supply. Soon, Hillsboro city residents will be the latest to chime in.

The City Council last month approved placing the measure on the November ballot that would advise the city’s water department whether or not residents want fluoride in their water. It’s already stirring up disagreement among some residents over dental care, health and freedom of choice.

The ballot measure comes amid a federal case in California in which the Food and Water Watch, a Washington D.C.-based advocacy group, is suing the Environmental Protection Agency, alleging fluoridation nationwide “presents an unreasonable risk” of harming the nervous system. The case could force the federal government to create a national rule regulating the use of fluoride in drinking water.

This is the first time Hillsboro residents have voted on fluoride in the city’s water supply since 1952, when voters passed it before a subsequent vote failed the following year. The debate has also raged for years in Portland, where voters have rejected it four different times, making it the largest city in the nation without fluoridated water.

Measure proponents say fluoride is critical for reducing cavities, particularly among children and low-income and marginalized people who may struggle to otherwise afford preventative dental care. They say having fluoride in the water can have lasting positive effects on people’s lives.

“This is not just a matter of having good dental health,” said Dr. Beth Mossman, a Hillsboro pediatrician and measure proponent. “This is a matter of graduating school, feeling confident in your smile when you’re there for a job interview or asking for a raise.”

Opponents voiced concern about the potential negative health effects to them, their children and environment. They said people should have the option to purchase fluoride in a store and choose if they want to use it or not.

“If you put it in the drinking water, you’re taking away the choice from a lot of people … This is a serious risk to human health. And it’s just not right to take away people’s choice whether to ingest a drug or not,” said Rick North, former CEO of the Oregon chapter of the American Cancer Society, who recently retired and moved to Massachusetts.

Fluoride is a naturally occurring mineral that’s added to drinking water in cities across the United States. Small amounts of it can reduce tooth decay, studies show.

And much like vaccines, the public debate over fluoride in drinking water has grown increasingly divisive. Both sides point to a number of studies and institutions in an effort to bolster their argument over its safety and efficacy and take aim at the other sides’ research, claiming it’s flawed.

Experts “have not found convincing scientific evidence linking community water fluoridation with any potential adverse health effect or systemic disorder” like cancer, Down syndrome, heart disease and more,” according to the Centers for Disease Control and Prevention. The federal agency says fluoridating the water also saves costs in dental treatment.

The National Institutes of Health, however, also says that excessive consumption of fluoride from dental products or dietary supplements can have negative effects. In very large amounts, this could include nausea, vomiting, abdominal pain, diarrhea and, among youths, dental problems.

If the measure is approved in Hillsboro, fluoridating the water would likely require about $4 million over five years, including design, permitting and construction, said Niki Iverson, the director of Hillsboro’s water department.

The most cost-effective option for the city would be to either work with other local governments through a local joint water treatment plant, or to fluoridate the water at a water tank or another location somewhere along the pipe system the city is building to connect to its future secondary water source along the Willamette River. Hillsboro currently gets its water from the upper Tualatin River and its tributaries.

Iverson said fluoridating the water would not impact ratepayers because the city would move around lower-priority projects to accommodate the development.

Many drinking water systems across the United States fluoridate their water. That includes the nearby cities of Beaverton and Forest Grove. Oddly enough, it also includes a chunk of Hillsboro residents.

The city’s water department serves more than 92,000 of the city’s roughly 108,000 residents. The remaining roughly 15,000 people are served by the Tualatin Valley Water District, which puts fluoride in the water.

Since June, some Hillsboro residents — as well as dentists and orthodontists from Portland and elsewhere — have written to the city, urging it not to put fluoride in the water.

Dr. Jay Levy, a Portland dentist, said research about fluoride is historically flawed and says large amounts ingested during childhood can lead to a rare condition called fluorosis, which can cause joint pain and stiffness, weak bones, muscle loss, and nerve problems.

“You’re going to turn a nice suburban place into a place full of toxicity,” said Levy. He added, “It just doesn’t make any sense.”

Meanwhile, some medical and dental professionals in and around Hillsboro also signed letters of support for fluoridating the water supply.

Mossman, the local pediatrician, said that she has noticed clear differences in dental health depending on whether communities are receiving water with fluoride. She says the kids without fluoride in their drinking water are more prone to cavities and other dental pain that may cause them to miss school and flunk out of school.

One family, whose parents work around the clock, had to sell their vehicle to afford dental care for their two children, who had nonverbal autism and whose dental health was beyond the point of repair without anesthesia or sedation, she said. She looked up their address. They lived less than a mile from a district with fluoridated water.

“That got me pretty fired up,” she said.

Fluoridating the water would be helpful especially for underserved kids with families who work around the clock, she said.

“Their parents aren’t even home when they go to bed. Their parents are out working,” Mossman said. “Who’s going to remind them to get their fluoride drops in?”