An estimated 30,000 homeowners across Ottawa are being urged to replace their old pipes after Health Canada issued new guidelines suggesting there's no acceptable amount of lead in drinking water.

Lead pipes were once the standard for household plumbing, but were gradually replaced by other materials starting in the mid-1950s.

"Lead pipes were used from the 1800s up until 1955 and, from our records at least, that is estimated to be 30,000 homes in Ottawa, which is roughly 15 per cent of the homes," Ian Douglas, a water quality engineer with the City of Ottawa, told CBC's Ottawa Morning.

The city offers homeowners a $1,000 rebate toward replacing their portion of the lead pipes connecting their homes to the water main, roughly 40 per cent of the typical replacement cost. The city remains responsible for replacing pipes up to the private property line.

Douglas said Ottawa's treated tap water is lead-free, but can pick up trace amounts of lead as it passes through old pipes leading into homes.

Ottawa's drinking water is top-notch, Ian Douglas says, but can pick up trace amounts of lead from the pipes leading to older homes. (Andrew Foote/CBC)

The city has $1 million set aside to replace its portion of the pipes, but at a cost of about $7,000 per property, it would cost approximately $210 million to replace all the pipes leading to the estimated 30,000 homes in Ottawa that still have lead, and would likely take years.

The city also offers a loan program to homeowners who want to replace their lead pipes, allowing them to pay off the cost along with their property taxes over several years.

Douglas said there was a spike of interest in the replacement program in 2007, when the issue last made headlines.

"The phone was ringing off the hook," he said, but interest has since waned.

Probable carcinogen

So, what makes lead so dangerous?

"There's been mounting research over the last 10 or 20 years that they can't find a safe level for lead, so even tiny amounts of lead seem to have an adverse effect," Douglas said.

According to Health Canada, those adverse effects include "reduced intelligence in children," reduced cognition, increased blood pressure and kidney problems in adults.

Lead has also been classified as a probable carcinogen.

The city is offering free testing for anyone who's concerned their tap water may contain lead, and is also offering free lead removal kits for a year.

"Kits are really effective, however, they're really an interim measure. So, for example, in the middle of the night, you know, a child gets up and is thirsty and takes a drink of water, they're probably not going to be using the filter," Douglas said.

"Really, the long-term solution is to remove the lead service pipe."