water is tap water that has been run through a reverse osmosis filter system. Without going into great detail (google search=reverse osmosis...tell you more than you want to know probably
water has had all the minerals and chemicals removed. It is at least 99% pure H20. No phosphate, nitrate, chlorine, ect... You can also use distilled water, but that can get expensive. The better RO
units also have a DI
(deionization) chamber that filters out anything the RO
membrane missed. It's available at most LFS
's and some grocery stores sell it. Don't mistake bottled spring water for RO
water...it's not the same.