I use RO water that I get from Gabe's or Texas Tropical. Buying a RO unit does not seem to make sense to me (Yet). Most stores sell Ro for .25 Cents or .35 Cents a gallon. With personal RO unit, first you buy the unit, maybe even install it, and then most units waste 3 gallons for each gallon of RO "made".

I might be wrong, I'm new to this too, but buying the water is easier.

As a note, I use this same RO water and add my own reef salt for water changes too.