I have a zero-waste reverse osmosis system under my kitchen sink (a Watts ZRO-4 specifically, though there are other systems to which this applies) and my house is also pre-plumbed for a softener in my garage. From what I've read, the "zero waste" portion of this system means that it still has waste water (like any other RO), but just that it pushes it into the hot water line rather than down the drain as other systems do.
I'd like to install a softener in my garage, but since the RO has hookups into both the hot and cold under my sink (the hot is softened and the cold is non-softened), I just want to make sure I won't end up with salty water into my RO. If the system consumes hot water at all (or even if it doesn't maintain proper pressure into the hot water line when it's not discarding waste), it seems like this is a risk.
It sounds like the system only pushes waste into the hot water line and doesn't actually consume hot water during operation, but can anybody confirm that these two systems (zero-waste RO and softener) can operate together without any issues?