Researchers at the University of New Brunswick have found a potential vulnerability in the water supply for the city of Fredericton.

Groundwater forms the drinking supply for more than 55,000 people in the city, as its reservoirs are pumped full by underground aquifers through 10 wells.

UNB researchers have found that water from the St. John River is moving into the water supply at several points, through weak spots in clay that separates the aquifer from the river.

"Those areas, which we call windows, would be areas where the river water directly infiltrates into the aquifer when the wells are pumping," said Kerry MacQuarrie, a civil engineering professor and the Canada research chair in groundwater and surface water interactions.

Those windows could make the water supply vulnerable to contaminants that might find their way into the river, which the water treatment system might not be equipped to handle, said the research team.

Kathy Edwards, Fredericton's wellfield protection officer, said the city has great confidence in its water supply and the new information may lead to ways to enhance protection of it.

"Awareness of the different aspects of hydrogeology, the movement of the water, and the aquifer itself, that growing awareness just allows us even more opportunity to find ways to protect our really pristine, wonderful water supply," she said.