I've been tossing around the idea of getting an R/O system. My tap water is quite hard (HCO3=457,CACO3=452) and when I've run it through a carbon filter and made beer, the results, for IPA anyway, aren't that great. I've been using distilled water for awhile now and quite pleased. My local grocer is having issues keeping distilled water stocked however. The shelf is missing all but a few gallons for the past month. Hard to tell how long it might last.
I've been looking at the Waterdrop 600GPD (update: I have the wrong number here. Model number is actually WD-G2P600-W) since it boasts a 2:1 drain ratio, which is nice, but the replacement filter cost is over $100 bucks which isn't so nice. I think there are actually two filters on this unit and from what I've been able to find, the second one is ~$30 so there's a substantial cost to running this.
If I use this just for brewing, and the other needs (netti pot) we use distilled for, the filters may last considerably longer than a standard installation. I brew maybe once or twice a month so leaving the system sit for a week or so may introduce other longevity concerns. Still need to look into that.
I poked around the forum a bit here and found a discussion with Martin from 2018 https://www.homebrewersassociation.org/forum/index.php?topic=32353
where another person mentioned the iSpring RCC7P was a favorable unit. Being a few years old though, things may have changed. Also sounds like feedwater from the R/O system should come from the output side of my water softener to cut the hardness. Maybe add a carbon filter too.
Are ya'll still liking your iSpring or other units? Any suggestions other than filter cost and drain ratio if you had to buy one again?