And although I try to avoid it, when I have to wash windows, RO water is the way to go. No spots.
Hopefully you still have a softener as pretreatment to that RO system. If not, you'll be going through membranes in short order. Unless maybe you're injecting an anti-scalant? That can work too.Our well water is over 4,000 ppm tds. Basically full of dissolved gypsum. It will dissolve granite (takes a while, but the effect is noticeable). Bought the house 5 years ago, replaced the existing softener system with whole house RO, which rocks. the brine/concentrate will kill most vegetation, so it is disposed of in the drainfield, bypassing the septic tank.
What do we use RO for? Everything. There is still a small amount of mineral content - made a Dry Irish Stout that came out near excellent last month.