mine just goes down the drain to be recycled through our sewage system to come back later. i keep a float valve on my reservoir so i can leave it to fill up while i'm gone for the day without worrying about a flood, but then i shut off the unit with ball valves at the product line and then at the source line, so the unit stays pressurized but is not producing waste water 24/7 when i'm getting no product water. my unit has a special valve that is supposed to shut off water flow through the unit when the pressure backs up in excess of 65 psi so the whole unit shuts down when the float valve stops it, but my water pressure isn't high enough so waste water still trickles out.