I've started buying the RO water at walmart at the fill it yourself station (culligan). $1.80 for 5 gallons. I get 10 gallons at a time.
Then I use the mineral additions in the water primer sticky. It has taken my quality up another notch. I have very hard water, and got tired of mixing tap with my home RO system at various ratios. It was also killing my RO filters fast which are expensive, so $3.60 is a bargain.