TRENTON — The fluoride is flowing once again.

Almost six weeks after two Lawrence councilmen angrily complained that Trenton Water Works never notified customers it had stopped adding fluoride to drinking water supplies, the city said fluoridation resumed this week.

“On Tuesday, April 14th, the water utility returned to its practice of adding one milligram of fluoride per liter of water,” Joseph McIntyre, general superintendent for water and sewer, said in a press release.

Fluoridation is not legally mandated in New Jersey, but fluoridated water helps prevent tooth decay and has been described as important to public health.

Trenton had been putting fluoride in the water that flows to the utility’s 61,000 city and suburban customers, but stopped last August when a supplier ran out of dry powder fluoride, McIntyre said last month.

By the time more dry fluoride arrived, in October, the utility was too far along in the process of switching to a liquid fluoride system to use the powder, he said.

The equipment switch came as part of an ongoing $55 million upgrade of the city’s water filtration plant.

Trenton Water Works had told the state Department of Environmental Protection that fluoridation would stop for just one or two months, but in February the agency found out fluoridation still hadn’t resumed, according to a Feb. 2 letter from the DEP.

CDC guidelines say a lack of fluoridation for one or two months should not result in “an immediate increase in tooth decay,” but it appeared the utility had “greatly exceeded” that duration, the letter said.

Last month Lawrence Councilmen Rick Miller and Bob Bostock were sharply critical of Trenton Mayor Douglas Palmer and Trenton Water Works for not notifying customers of the extended lack of fluoridation.

Children may be given drops or dental treatment to substitute for a lack of fluoride in water, but parents and dentists had no idea the fluoridation had been stopped for so long, they said.

Trenton Water Works had planned to resume fluoridation by May 1 but was able to begin sooner, according to McIntyre and Public Works director Eric Jackson.

The city notified DEP, Mercer County’s health communication system and the townships of the resumption, they said.

In February the Assembly Health Committee approved a bill that would require all of the state’s public water supplies be treated with fluoride.

Only about 22 percent of the state’s residents get fluoride-treated water from their tap, one of the lowest rates in the nation, according to the NJ Dental Association. Newark, Camden, Paterson and Atlantic City do not add fluoride.

The Assembly bill is strongly supported by the NJ Dental Association but opposed by water companies and some environmentalists, who say impure or excessive fluoride could hurt water consumers and riverbeds.