Toronto is spending $250 million to replace its old lead water pipes. (CBC)

Toronto Public Health says it is investigating research done by an American scientist into the partial replacement of residential water pipes.

Toronto is in the midst of a five-year, $250-million lead pipe replacement program — but the city only replaces the pipes on city-owned land. It's up to homeowners to pay to replace the pipes that lead from the property line into their homes and in many cases residents don't replace the old lead pipes.

The city estimates that in about half the cases, people don't pay the several thousand dollars it costs to have their pipes replaced.

But research conducted by Mark Edwards at Virginia Tech University shows lead levels could spike if only part of the pipe is replaced.

"[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," he said in an interview with CBC News last week.

Edwards says when the new copper pipes are joined to the existing lead pipes the lead 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 Edward's research, which is undergoing final peer review.

Dr. Howard Shapiro, associate medical officer of health for the City of Toronto says Toronto Public Health has been in contact with Edwards for months.

"We've taken the position now that partial replacement is not a solution for people to mitigate their risk from lead," Shapiro said. "That's one of the things that followed from our discussion with Dr. Edwards."

Shapiro says the next step is testing the effects of partial replacements in Toronto.

"What we are doing now with Toronto Water is discussing, or considering, what's happening in Toronto when partial service lines are replaced." Shapiro says so far, no test has been developed.

Coun. Glenn De Baeremaeker, head of the city's public works committee, said last week the evidence he has is that even partial replacement is effective.

"The City of Toronto tests have always shown that once we replace the pipes in front of your house the amount of lead in your water goes down. We have found that consistently for two decades. So this is new information that we've never heard before," he said.

De Baeremaeker says the city will continue its lead pipe replacement program.