If the home is occupied, consider letting the water run/trickle rather
than shutting it off. You will have toilets to flush, water to drink
and wash with. Water coming from a city supply will be cold but not
If the home will not be occupied, then it's time to shut off the water
supply, drain water heater tanks, leave all the faucets open and put
antifreeze in the toilet bowl and tank. Don't forget the washing
machine and water remaining in the pump.
Other have already listed alternative heat sources: heaters, ovens,
stoves, fireplaces, etc. being careful of carbon dioxide or carbon
monoxide risks. Leave cabinets with water supplies on outside walls
open so that some heat can get in there.