The city's water utility could be forced to postpone major projects after an unexpected deluge of 50,000 residents signed up to have their downspouts disconnected on the city's tab before last night's deadline.

Toronto Water estimated it could cost as much as $65-million -- or the equivalent of a 10% increase in water rates -- to unhook that many downspouts from the city's combined sewer system.

"I'm very surprised at the number of calls we've received, particularly in the last two days," said Lou Di Gironimo, the general manager of Toronto Water. "They've both been in excess of 10,000 calls each day."

Mr. Di Gironimo said the utility would have to consider putting off projects such as reducing the odour at wastewater treatment plants and installing meters in homes paying a flat rate for water to cover the downspout bill.

Toronto City Council voted 29-7 to force as many as 120,000 homeowners to unhook at their own expense the pipes that carry rainwater from their roofs to combined sanitary and stormwater sewers. Residents have three years to comply before they face fines. The penalties have not been set yet.

Although yesterday's debate was technically about making disconnection mandatory, councillors spent hours wrestling with how to pay for the surprise costs of extending by three weeks the cut-off to qualify for the old voluntary program.

Toronto Water staff originally recommended that the city close the sign-up list for the free program on Oct. 31, but the public works committee voted the same day to postpone the deadline to notify residents.

At the time, staff predicted the utility could afford a surge in sign-ups. They were caught off-guard by the tens of thousands of people who called and e-mailed to get on the list.

"I have to be quite frank that I regret a little bit the way we handled this," Councillor Adam Giambrone, the vice-chairman of the works committee, conceded during the debate. "I think, had we known, we might have done it a little bit differently."

Councillor Mike Del Grande tried to move several motions restricting the amount the city would have to pay to cover the last-minute flood of sign-ups, but he withdrew the motions after other councillors criticized his idea.

"If these guys want to spend $65-million on this is it any wonder that people don't have confidence in the city?" Mr. Del Grande said in an interview after the vote. "Is it wrong for this council to say, 'We made a mistake, OK?' We can't afford it."

The city has had a free, voluntary downspout disconnection program in place for nearly a decade. Between 2,000 and 2,500 households have signed up annually. Mr. Di Gironimo said it costs the city about $1,300 per disconnection or roughly $3-million annually.

In recent years, severe thunderstorms -- particularly the Aug. 19, 2005, storm that washed out part of Finch Avenue -- have overwhelmed the sewer system, causing it to deluge basements with rain and toilet water. Disconnecting downspouts would help mitigate the problem.

"This is called prevention and prevention is always better than cure," Councillor Glenn De Baeremaeker, the chairman of the works committee, said.

Toronto Water will report back to the works committee in January about how it plans to pay for unexpected costs of the program.