For kits RO water would be excellent to make them up, although your tap water should be so low in dissolved minerals it should be pretty good on its own . . . once you have neutralised the chlorine with a campden tablet per 5 gallons. The reason the pH from the tap is so high is that the water authorities raise it artificially to prevent damage to pipes . . .although as copper is becoming a thing of the past these days it won't be long before they no longer have to do this :lol:
You would not want to use RO water if you were brewing all grain however.
You might find adding a tsp of gypsum to the FV along with the kit while you make it up beneficial to aid clearing and fermentation. (Calcium is a requirement, and while the extract manufacturer should have got things right for the mash water treatment wise I sometime have my doubts
