Thursday morning, a water main break on Gerrard Street in Toronto’s east end created a sinkhole over two metres deep that trapped a taxi cab. This past weekend, another water main break shut down the subway at Union Station.
While most of Toronto’s water main breaks are not this dramatic or destructive, they’re anything but rare.
On an average winter’s day, the city can count on having about seven or eight water main breaks, according to the Manager of Toronto Water, Lou Di Gironimo.
During a particularly cold winter, he said, that number can go up to 15 or 20 breaks per day.
The map below shows the number of water main breaks in Toronto between 2001 and 2011, broken down by ward.
Global News obtained records of the date and location of every water main break in the City of Toronto from January 1, 1990 to December 31, 2011. The records show that breaks are frequent – 1115 in the year 2011 alone, and that they are concentrated within a few areas of the city.
Ward 2, Etobicoke North, holds the title of Toronto’s wettest ward, with 699 breaks between 1990 and 2011. Water main breaks are most frequent in the Etobicoke and North York areas of the city and relatively infrequent towards the center of the city.
So what does it take to break a water main? A few things. Cold weather helps. After a few weeks of sub-zero temperatures, said Di Gironimo, frost penetrates the ground, making it hard. As trucks and other large vehicles drive overhead, their vibrations are felt deeper in the frozen earth, shaking the pipes.
This helps explain why breaks are most frequent in winter.
Explaining why some neighbourhoods have more blown pipes than others is a little more complex.
The type of pipe matters quite a bit, said Di Gironimo. “Depending on the thickness of the pipe material, the type of metal used, the manufacturing technology used, you may end up with a pipe that’s a little more brittle than other ones.”
Downtown Toronto is filled with hundred-year old cast iron pipes, that as long as they remain undisturbed, are still functional and intact.
But in the 1950s and early 1960s, said Di Gironimo, thin-walled ductile iron pipes were being placed into Toronto’s new suburbs. There, they ran into problems.
“We have clay soils in our suburbs. Clay soils are much more acidic,” he said. “When you have different metals in acidic soils, you get an electrical reaction, kind of like a battery. And you get corrosion.”
So, in the west and north of the city, weak pipes were buried in acidic soil, which causes them to corrode faster than elsewhere – leading to much more frequent water main breaks. Downtown, thicker pipes were put into sandy soil, so they have lasted a century.
Fixing a water main isn’t cheap. An average break on a 6-inch water main on a residential street costs the city between $5000-8000, mostly to repair the roadway that the leak has damaged, said Di Gironimo. Toronto Water’s annual water main emergency repair budget is between $5-6 million per year.
The city is working on preventative maintenance to make existing pipes last longer, and replacing kilometers of pipes that need it.
It seems to be working. Water main breaks have generally been trending downward over the last few years, from a high of 2174 in 1994 to 1115 in 2011.
“Over the past seven years, we’ve raised water rates nine per cent every year, and we plan to do it a couple more years, all of it to generate an annual revenue to do more capital,” said Di Gironimo. Revenue from water rates goes toward repairing and replacing water mains, as well as sewer and water treatment infrastructure.
“In the city, we estimate that we have a backlog of about $1.6 billion in our water-wastewater infrastructure. So we have to catch up on that. Once we do catch up on that, and that’s going to take probably about 8 to 10 years, we then have to invest enough every year to deal with what is the natural aging cycle.”
“This infrastructure has got to last us. As long as we live in this city, we’ve got to keep replacing it.”
Chart: Number of water main breaks in Toronto 1990-2011
Source: Freedom of information request, City of Toronto