I participated in this kind of discussion in a chat room a little while ago. One person says they "re-use" all the water. I got extremely curious and asked how he does it. This is what he told me.
When he first set up his tanks, 3 55 gallon tanks, he too was concerned about the water going to waste every week. He didn't have a flower bed, or garden that could benefit from the water. So he setup a return tank next to his RO/DI tank.
Water from the tanks gets drained into the "return tank". Close that valve, open the RO/DI tank and fills the tanks, then closes that valve. Then, he goes out to his tanks and turns on his RO/DI system. The system is supplied directly from return tank (with booster pump of course), and the water that doesn't go through the filter goes right back into the return tank, so no water gets wasted.
Thus creating a closed loop, and basically giving him a 1:1 system. He mentioned he has been doing this for years and has had no problems, diseases, or anything else out of the norm this way.
Has anyone else thought about doing something like this? I'm too chicken @#$$ to try something new like that.