Water is fine, I sometimes leave mine outside over night and it doesn't freeze and I couldn't be bothered using anti freeze. Oil gives it a really slow slugish feel which is horrible. Bottled water is not going to make much difference to normal water really depending on where you live. You would be better of distilling the water in a pan first so there is less air in it, won't make much difference though. The only down side is that your warranty doesn't cover it being filled with water.