The city of Montreal is warning pregnant women and young children to abstain from drinking tap water in certain areas because of trace levels of lead.

Some older homes in the Plateau Mont-Royal, Notre-Dame-de-Grace and Villeray districts are still serviced by lead pipes that are slowly leaching the element into potable water, according to tests conducted by the city last summer on 1,500 houses.

The tests found the majority of homes within the allowable limit.

The risk is minimal but the city doesn't want to take any chances, said Dr. John Carsley, director of Montreal's public health department.

At the end of February, it began sending letters to about 400,000 households warning residents the pipes connecting their homes to the main water system may be made of lead, and recommended children under six and pregnant women drink filtered water for the time being.

Montreal water itself is clean, but it could become contaminated with lead if left standing in the pipes that connect residences to the municipal system. 

The city is slowly replacing lead pipes remaining in the island's water system, but retrofitting will take another two decades, municipal officials said.

In the meantime people should consider switching to filtered water, Carsley told CBC News.

"We don't think it's a public health danger … but our objectives in public health is always to reduce the exposure to lead from whatever source."

"The risks are minimal but we recommend that everybody adhere to the norms."

The maximum allowable concentration for lead in Quebec is 0.010 mg per litre.

According to the public health department's website, "In some homes of fewer than 8 living units built prior to 1970 and linked to the municipal aqueduct system through a lead service connection, the tap water may exceed the standard."

Tap water treated with with commercially available filters such as faucet-mounted filters or filter pitchers certified by the NSF for lead reduction should be safe, the public health department said.

There has never been a case of lead poisoning from Montreal's water supply, Carsley said. Residents with concerns can call the city's water information line at 514-868-4483.