Well you don't have to worry about it dropping your temps unless you have your Ceramic heat emitter, UTH, or just plain lamp bulb on a thermostat to keep the temps from falling when the fogger cuts on.

Well you could run tap water in them, I've seen reviews of guys running it, and they said the foggers normally lasted 4-6 months running all the time with tap water. I don't know the life expectancy using the recommend distilled water.