The Metropolitan Water District of Southern California on Monday will start pumping fluoride into Orange County’s water supply.

MWD Spokesman Bob Muir said the fluoride injection system at the Robert B. Diemer Filtration plant in Yorba Linda is ready. Diemer supplies about half of the drinking water in Orange County.

Fountain Valley and Huntington Beach have been the only communities in the county with fluoridated water.

The Diemer plant is the second-to-last MWD plant to go online with the chemical, advocated by dentists and doctors who say it promotes healthy teeth.

Muir acknowledged the concerns of some national groups and community members who say fluoride is actually harmful to health, but he pointed out that it was a consortium of dentists and medical doctors who approached the MWD board and asked it to fluoridate Southern California’s water supply in the first place.

“There are pockets of the community that have questions and concerns about fluoridation,” he said. “This is being done at the request of dentists and doctors throughout the region.”

Muir says he often has to deal with angry customers complaining about fluoridation. Many county residents, however, aren’t worried.

“I would assume if it’s being done, it’s being done to improve the quality of our teeth,” said Joe Carey, 46, of Rancho Santa Margarita. “If it ultimately does that, I don’t have a problem with it.”

“I’m definitely for it,” said Bill Mitchell, 83, of Placentia. “I think it’s a great preventative and I don’t have any problem with it.”

Who gets fluoride?

When the Metropolitan Water District of Southern California starts adding fluoride to its water in November, some of Orange County’s 3.2 million users will get fully fluoridated water. Others will get none and still others will get a mix of fluoridated and nonfluoridated water. Below is a breakdown of where the water goes, listed by water provider.

All customers will get fully fluoridated water:

El Toro Water District

Emerald Bay Service District

Laguna Beach CWE

Moulton Niguel Water District

South Coast Water District

Santa Margarita Water District

Some customers will get fully fluoridated water:

City of Anaheim

City of Brea

City of Buena Park

East Orange County Water District

City of Fullerton

City of Garden Grove

Golden State Water Company

Irvine Ranch Water District

City of La Habra

City of La Palma

MesaConsolidated

City of Newport Beach

City of Orange

OrangeParkAcres Mutual

San Clemente

San Juan Capistrano

City of Santa Ana

City of Seal Beach

Serrano Water District

Trabuco Canyon Water District

City of Tustin

City of Westminster

Yorba Linda Water District

All customers already get fully fluoridated water:

City of Fountain Valley

City of Huntington Beach