definately do the calcs, but also keep in mind that RO water is not RO/DI water... andyes, our fish deserve better water then we do, as that is thier life.. thier air... if we were as sensitive as our fish you certainly wouldnt want to import Los Angeles air for us to breathe but rather filtered air...
but i am guessin you knew that and your comment was totally in jest...
and yes, ro/di filters 'waste' water.. that is it takes 3-4 gallons of tap water to make 1 gallon of filtered water... if you dont plumb your filter to 'recycle ' the waste water then that water goes down the drain.. but you can just run a small tube out to the planter, or into your waashing machine, or you can buy a system that plumbs it back into your home, *into the hot water system,.... as we dont drink hot water...
and the waste water is just a little concentrated tap water... nothing more...