Residents of White Rock, B.C., are being urged to boil drinking water following the discovery of E. coli bacteria in the Vancouver suburb's water treatment system.

The Fraser Health Authority issued the boil water notice Friday night after the contamination was detected at a residential sampling point on Tuesday. Testing and analysis of samples from other sites over the next two days confirmed the initial finding, leading to the boil water notice.

"Residents on the municipal water supply should be boiling their water if they are going to be using it for drinking, brushing their teeth, making formula for babies [or] making ice," authority spokesman David Plug said.

"There were coliform [bacteria] detected as well as E. coli bacteria, so, as you know, E. coli can lead to serious and sometimes fatal cases in people," Plug said. "However, most people that get sick don't notice the symptoms. The symptoms to look out for are bloody diarrhea and [stomach] pains."

Epcor, the company that runs the water treatment system, is puzzled by the source of the contamination. "Typically, if you look at other situations, it's at the wellhead or there is a break in the system or there is something in the reservoir," said company spokesman David Rector. "It's certain things like that.

"In this case, for example, a mouse could have gotten into the system and done that or it could be a break in the system that we are unaware of."

Crews are testing and flushing the system, Rector said, but it could take up to a week to make sure the water is safe. The advisory will remain in effect for at least a week.

About 80 homes in South Surrey along 16th Avenue are also affected by the boil water order.

With files from the CBC's Emily Elias