New research by a U.S. water expert says homeowners who don't replace the lead pipes leading into their homes are taking a risk.

In Toronto, a multi-million dollar lead pipe replacement program is underway, with the city replacing the aged lead pipes that supply residential properties. The city will replace the pipe from the street up to the property line, leaving homeowners the option of paying to replace pipes on their side.

Marc Edwards, an environmental engineer at Virginia Tech University, says replacing only a portion of the lead plumbing heading into a house is dangerous.

"[Replacing] half the lead pipe, in some cases, makes the problem worse. There is strong evidence emerging that this is a serious and long-term problem."

The city estimates about half of homeowners don't have the lead pipes on their side of the property line replaced.

Edwards says when the new copper pipes are joined to the existing lead pipes the lead rusts and occasionally flakes off into the water causing extraordinarily high lead concentrations.

"As it accumulates and water passes by that copper-lead connection, every now and then some of this rust can fall off and it can fall off at extraordinary high concentrations," he said.

In the U.S. similar lead pipe replacement programs have been halted, mainly because of Edwards's research, which is undergoing final peer review.

Glenn De Baeremaeker, chair of the Toronto public works committee, says keeping lead pipes is not an option. "We are going to spend about $250 million over the next five years to make sure we get out our lead pipes."

"We just can't legislate common sense and safety," he said. "I would encourage anyone with lead pipes in their house to get rid of them as soon as is humanly possible."

Etobicoke resident Peter Tomzak is in the process of having his lawn torn up while the city replaces the lead pipes leading up to his property line. Soon he'll have to make a decision on the rest of the connection.

"I just found that the quote that I got here was a little bit on the high side. So it's now going to be up to me to decide whether I want to to do it or not," he said.

Tomzak says he's facing a bill of about $4,000 in order to complete the project.

De Baeremaeker says the city does not intend to change its program for the time being.

The water department and city health officials say they will wait for the final results of Edwards's study before making a final decision.