Work began today to construct Mount Gambier's fluoridation plant, with fluoride expected to be added to the water supply next year.

Excavators began preparing for where the plant will be built, on the side of the road, just up from the pumping station.

SA Water says it'll take five months for the works to be completed.

"We anticipate residents will start receiving a fluoridated water supply by mid-2010," SA Water's chief operating officer John Ringham said in a statement.

"From today, contractors will start preparing the construction site with the majority of major works to start in late December."

The installation of the fluoridation plant is much later than expected, with SA Water saying earlier this year that it hoped to have the plant installed during November.

But few residents have been complaining about the delay, with some still holding reservations about the State Government's plan to add fluoride to the water supply.

"And this is supposed to be a democracy," said one resident as they heard the news that construction had begun.

Earlier this year SA Water wrote to residents confirming its fluoride plan, describing fluoride as a "repair kit for teeth".

"Fluoride can limit the amount of damage and can repair the damage before a filling is needed," the health sheet said.

"Strong teeth result in fewer fillings, fewer extractions, fewer visits to the dentists and lower dental bills - resulting in healthy smiles and fewer dentures.

"Mount Gambier is the largest centre in South Australia without water fluoridation."

SA Water says it will write to its customers when the plant's construction has been completed and is ready to start delivering fluoridated water.