Every time we leave the house for a few weeks, I have visions of coming back
to a house that has been flooded from either a burst water heater or two (in
the attic) or burst pipes from a freeze.

As a precaution,I have considered turning off the water at the outside
shut-off and draining the pipes inside by opening the faucets.

What disasters lurk in this procedure? Can I just return home, turn on the
water and sputter the air out of the pipes, or is there some fundamental
embuggerance that I am overlooking? Will this require re-lighting the gas
in the water heater?