CHICAGO (CBS) — Chicago water mains have been doing fine in the subzero weather, but the temperatures have been tough on the fire hydrants.

City Water Commissioner Thomas Powers said he’s keeping two crews on standby at all times with steam trucks to accompany fire crews. Powers said the steam truck will thaw the hydrants quickly, and let fire crews attack the flames.

The water mains are usually buried deep enough that they’re insulated from subzero temperatures by surrounding soil, according to Powers.

He said three mains ruptured in the 24 hours from Monday through Tuesday morning: at State and Ontario, at 35th and Western, and at 53rd and Harlem.

The repairs are straightforward, but take longer than normal because of the need to pump out the pit, and rotate crews frequently in the cold weather, Powers said.

The city has 12 to 16 leak crews on duty during the day, and three leak crews in the evening and overnight, along with two hydrant crews ready around the clock to assist fire crews on call, according to Powers.

He was asking two things from Chicagoans during the subzero spell:

1. Keep at least one faucet in the house trickling all night so the flow will continue, and prevent icing of water lines into the house.

2. Use nothing hotter than a hair drier to thaw out frozen water lines. Powers said open flames like hand welding torches are known to start fires.

Powers said the city has 4,500 miles of water mains. Of those, 1,000 miles are 100 years old or older.

The city has replaced 150 miles of water mains in the last two years, but Powers said the cold itself has not been breaking an unusually high number of water mains.

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