A water heater can burn otu the bottom of the tank if the tank goes dry.
This is unlikely with turning the water off, but leaving the gas on.
(assuming you leave the water in the tank, and don't open the drain at the
"evaporate it all out", well, where is the vapor going to go? From water to
vapor, the volume expands times 1800. And it's a sealed system, not like a
soup kettle which is open on top.
But why take the chance? I suggest either leave the water on, or turn them
both off. Of coruse, the relighting problem. Got any neighbors to relight it
for you? Relatives?
Christopher A. Young
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