You can use any water you like. If it isnt RO, or distilled, it will eventually build up deposits on the transducer though. This can be cleaned off with white vinegar. I know of no other issues.
Agreed, groundwater that has not had it's dissolved minerals removed (i.e., everything other than distilled or RO/DI) will leave mineral deposits in the machine and as a fine dust. For one day I wouldn't be worried about the mineral buildup much (though the fine dust could be irritating for the animals), though for one day I'd probably just leave the machine off
Ok thats what I was thinking ill only be gone a few hours, im graduating highschool tomorrow lol. Then ill be home to take care of him. Thanks for the responds.