I personally use RO
water from my RO
unit. Some people use tap water with good results. Others have bad results because their water leaves very much to be desired.
IF your on city water then you need to condition it with declornator first.
I think you will find many RO
units are rather afordable. Look at it as an investment in not only your ability ot make quatlity water for your evaporation, water changes you can also use for your drinking water.
Everyone who visits prases how well my water is.