I think it's just depends on various factors. Weight, CsA dosage, but mostly on labs (Creatinine). My son aims for at least a gallon daily plus any other food choices that are hydrating. We just try to monitor this as best as we can, but usually see-saw.
BTW, I sound like a broken record always asking if he's been drinking enough
Sad, but true
http://www.livestrong.com/article/28...water-content/