Waving aside threats of litigation from its smaller neighbors and a possible legislative battle in Richmond, Fairfax County’s Board of Supervisors voted Tuesday to set water-service rates for all county residents, including those who get their water from municipalities such as the city of Falls Church.

Beginning next July, a municipal utility that set higher rates than those set by Fairfax Water would have to demonstrate why the higher rates are justified.

The board’s unanimous vote to amend the water ordinance also allows the county to establish exclusive service areas for Fairfax Water, the county-controlled utility that supplies most water in the county, effective Wednesday.

The move comes after years of sparring — including a legal battle — between the county’s water authority and the municipal utilities operated by some of its smaller neighbors.

“This has been a long time coming,” Chairman Sharon Bulova (D) said. She argued that the county had no choice but to protect county consumers who were paying much higher rates for municipal water than neighbors who receive Fairfax Water.

The board’s action also tracked recommendations from the county’s Consumer Protection Commission following a study that said Falls Church’s municipal water utility imposed excessive water rates on customers outside its borders that made them victims of taxation without representation.

“Let’s pull the plug on the ATM machine,” said Kirk F. Randall, a resident who urged the board to act because he and his McLean neighbors had no other way of fighting back against Falls Church water rates.

But officials from Falls Church, Vienna and Fairfax have criticized the county’s action as heavy-handed, with some saying the county wants a water monopoly in order to benefit from millions of dollars in revenue from thirsty new development in Tysons Corner and Merrifield.

Falls Church officials have said the city has supplied some nearby county residents with water since the 1930s and that city and county residents have paid the same rate for Falls Church water since the 1970s. City officials also said the rates they charge both city and county residents fairly reflect the investments that its residents have made in the water system.

Falls Church Mayor Nader Baroukh said the city had asked the board to defer action to work out an amicable solution. “Instead, the board chose to rush to enact an ordinance that is anticompetitive and not in the best interests of our county water customers,” Baroukh said.

Supervisors John C. Cook (R-Braddock) and Pat S. Herrity (R-Springfield) expressed concern that the county’s move risked increasing friction and litigation with its neighbors. But both ultimately supported the measure.

The action sets Northern Virginia’s largest jurisdiction on a potential collision course not only with its smaller neighbors but also with one of its state lawmakers. Sen. J. Chapman “Chap” Petersen (D-Fairfax) said Friday that he is drafting legislation that would prevent the county from interfering with existing water service agreements between municipal providers and their customers.

The immediate dispute arose from the city of Falls Church’s treatment of customers who live in Fairfax County but receive water service from the City of Falls Church. The city’s water utility serves about 34,000 accounts, and 90 percent of those are in Fairfax County.