Hi everyone, My new water heater states: "Install vacuum relief in cold water inlet line as required by local codes". My inspector says I need one. I read on one of the old posts that you only need one if your water heater is on an upper floor or in the attic. Mine is in the attic. What is the purpose of a vacuum relief valve? What could possibly happen if I didn't install one - other than the inspector killing me? Thanks in advance for your help.