I want to shut off my water supply while I am on vacation. I plan to put the gas control valve on "pilot" while I am gone, and let the pilot continue to burn. Is this OK? Should I open a hot water faucet in the house to relieve any possible pressure buildup due to thermal expansion? The heater is located in my attic in Houston, Texas. In summer, the attic temperature can be as high as 110 deg. F

If turning the water off means shutting a valve off at the water meter, and you don't have an expansion tank, yes you must do something. Back flow preventers and expansion tanks are now required on many systems. If it means throwing the breaker on a pump, and leaving the pressure tank open to the hot water heater, no problem.

In most cases, turning the tank to pilot will be enough even saving a little gas. Opening a hot water tap gives a little extra protection. Note, if it is open to a pressure tank, doing so will empty the tank unless you shut off a valve.