High levels of trihalomethanes detected in the water of residents living on the west side of Saint John this week show the need to improve the city's water supply, say officials.

Though the water is still safe to drink, officials at Saint John water and sewer department said Wednesday the elevated levels of the cancer-causing chemicals wouldn't be present if a proper filtration system was in place in the city.

"Chlorinating our water is the only safeguard we have in place," said Brent McGovern, Saint John water and sewer manager.

Installing a treatment system with full filtration is years off, said McGovern, and would require money and political will. City hall is currently reviewing design options for a new plant but the earliest possible completion date is 2012.

The current system has no safeguards if the chlorination fails, said Dr. Scott Giffin, a medical officer of health for Region 2 in Saint John.

"The chlorination system is rigged with alarms so if it fails, it should alarm. But we've already had episodes in which that didn't happen," said Giffin.

"And when you have something like a lightning strike, that can disable these sort of things and it can be some time before anybody knows we're not getting chlorinated water."

The city needs a full water treatment facility as soon as possible, he said.

Water is supplied to the city from Spruce Lake and Loch Lomond Lake and is susceptible to contamination from animals, human dumping, the nearby airport and roads.

"If there was some sort of accident that happened that ended up in the water supply, then we'd have no way to manage that without letting it come through the system," said Giffin.