I have mentioned this many times on many boards but probably not here... RO water can be all over the place. Many brewers have told me that RO water is close enough to distilled water that you should just treat it like distilled. I'm sure that's true in some cases. I used to get bulk RO water from the grocery store... bring empty, blue 5-gallon bottles and fill it up. I was treating it like distilled but my results were really discouraging. I took some of that RO water and sent it to Ward Labs and found that there were still some high numbers including bicarbonate at 50ppm, high dissolved solids, etc. I'm sure that most homebrewers who have an RO system in their home are careful about system maintenance, etc. The point is that distilled should be pretty much ZERO across the board while RO may have numbers that are higher.