February 22, 2005

Larger the pipe, bigger the leak

Like the power grid, watermains have a distribution system and transmission system. The power blackout that crippled areas from Ohio to Ottawa in 2003 was a transmission main failure. The watermain breaks that occur almost daily in Toronto are failures in the water distribution system.

If a transmission pipe ever has a major break, “the consequences are very high,” says Dr. Balvant Rajani, senior research officer, Buried Utilities, with the Institute for Research in Construction.

“The consequences for failure in a large pipe is tremendous because it would shut down the fire stations, shut down the houses, the factories, the manufacturing capabilities, the hospitals, the schools; everything breaks down.”

There are two types of larger diameter watermains, says Sam Morra, executive director of the Ontario Sewer and Watermain Construction Association. The mid-range ones are about a metre in diameter and are made of cast iron. “We’ve seen some significant consequences in the city when they have broken.”

The larger ones are 1.5 metres in diameter or larger. “It is typically steel pipe that is concrete encased. I don’t know what sort of maintenance or rehabilitation plans they have for them. My understanding is that they haven’t had many failures with those very large diameter watermains.”

Rajani says there are only about five of the larger transmission mains in the entire city.

“If one of these were to break, that means 20 per cent of the water is gone. . . . These large pipes are not inspected. First, there’s not the technology to inspect them without interruption. Imagine the mayor of Toronto saying, ‘Tomorrow, 20 per cent of Toronto won’t have water for two days.’ What would the reaction be? . . . So, they manage this system, basically, nervously because these pipes have got older and older.”

He says the pipes age might range from 80 years old to 30 or 40 years old.

“I’m sure they do break,” he says, but more infrequently than the distribution pipes because they are better structurally designed. “They don’t tell you about it,” he says, because the public would be concerned. He suggests the city could use its reservoir capacity to repair a break immediately.

But he doesn’t sound an alarm that the city is in risk of a watermain blackout equivalent. “The fact that Toronto has never had water failures must mean it is in good hands.”

— Peggy Hill

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