Silicon Valley’s biggest water provider took another step this week toward treating the drinking supply with fluoride.

A committee of the Santa Clara Valley Water District board voted 3-0 Monday on a recommendation to fund fluoridation at its three water treatment plants. The plan calls for the water district to spend $4.2 million while the remaining $2.4 million is being funded by outside sources.

The plan now goes to the full board for a vote that could happen as soon as its Dec. 11 meeting.

“The decision about fluoridation already has been made,” said board chairwoman Linda LeZotte. “This is the funding mechanism. There may be some tweaks, but I think there are at least four votes there to pass this.”

In November 2011, the water district board voted 7-0 in support of a fluoridation program. The committee was formed to come up with an implementation plan and work with community groups to pay for the project.

The committee decided there was no need to fluoridate the Campbell Well Field emergency water supply. The cost at the three plants is estimated at $6.6 million.

The Health Trust ($1 million), First 5 Santa Clara County ($900,000) and the California Dental Association Foundation ($500,000) are combining to chip in the $2.4 million.

Supporters, including public health officials, say fluoridation reduces tooth decay — especially for low-income children who don’t have access to dental care.

Only 21 percent of Santa Clara County residents have fluoridated water, compared to 72 percent of U.S. residents. San Jose is the country’s largest city where all residents don’t have fluoridated water.

In the past, though, there has been resistance on the board to spending money on treating water with fluoride. Also, critics continue to contend that fluoridation adds unnecessary costs and can lead to health ailments. But on Monday, board members LeZotte, Tony Estremera and Don Gage voted to recommend funding.

The unanimous vote sends a strong signal because the makeup of the board is about to change, advocates say. Barbara Keegan and Nai Hsueh were elected earlier this month, and their first meeting will be on Dec. 11. Gage also was just elected Gilroy’s mayor and is leaving the board.

“The vote shows that the board understands this is settled science and there is no controversy here at all,” said Frederick J. Ferrer, CEO of the Health Trust. “This is a safe, cost-effective way to solve a health problem with a public-private partnership.”