About 50 residents of a senior's home were relocated to another part of their residence. Several nearby buildings were likewise evacuated.
A spokesman for the city said the situation was being stabilized and the leak was almost stopped by early this afternoon.
He said the reservoir was not structurally compromised and the holes were likely caused by ice buildup around a pipe.
The spokesman said the city's drinking water supply is safe, although close to 4.5 million litres are believed to have been lost.