Dialysate in a conventional system does not run through the dialyzer many times. Fresh water is purifed by a reverse osmosis water purifier, then through the ultrapure filter. Then it enters the dialysis machine where it is mixed with bicarbonate and acidified concentrates to form the required dialysate. It only runs through the dialyzer once and then it goes out the drain. Some dialysis centers may have some kind of water recovery system, but you don’t have this at home.
Dialysate flow rate for short daily hemo is usually 500.
Even NxStage must start with water. Whether the water is purified to “ultrapure” standard at a factory or on site doesn’t matter in the end.
Pierre