Well said. To be green, and, equally important, cost-effective, store and use the "waste" water for other purposes - laundry or gardening.
Something is strange here, but I need to wait until he posts more information before I can comment.
Strange things: reverse osmosis does not remove impurities from water. It removes clean water from impurities. You have to let the impurities goes SOMEWHERE - it is not like they are being collected somewhere like in mechanical filtration. If you want to go green just run your waste water line into your yard/garden. Problem solved.
DI removes different things from water than reverse osmosis. As its name implies, it de-ionizes the water by removing mineral ions like sodium, calcium, iron, (cations) and chlorides and bromides (anions). It is complementary to reverse osmosis; it does completely different things.
Why are you running UV in your storage tanks to "prevent mold"? If your water filtration system is working well the water should be close to distilled quality and have ZERO organics. There should be nothing in the water to grow mold.
Personally, I hear a LOT of work being done with lots of filter changes, filter media used, electricity used, etc, just to avoid running some waste water into your yard. Where do you think filter media comes from? How is your electricity generated? If either of these answers is less green than running 100 gallons of waste water into your garden each week, I think you are heading down the wrong path. If you want to save water, just take shorter showers
