Hopefully Martin or Carl (where the heck is carl anyway?) will respond with better info but I believe that alot of the systems have like a 90% rejection rate. so it takes 10 gallons to make 1 gallon. now, that water doesn't just disapear and I imagine it can go lots of places. it's only 10% more hard than it was when it came in so you can use it for lot's of things I would think, depending on how hard it is to start. watering plants if nothing else.