Depending on how good or bad your incoming water is, you may even be able to drink it, though I wouldn't try. If your water isn't that bad to start, it's not going to be much worse as waste water. Some folks water their gardens, some use it washing their laundry. If it's 2-1 (2 gals waste for every 1 gal RODI produced) It's should have about 1.5x the original concentration of contaminants, or, half of the total contaminants of the three original gallons of water, less the stuff permanently trapped in your filters. You could easily wash your dishes with it and rinse them with tap water, probably even bathe with it, unless your tap water is so bad that it's borderline unsafe to drink to begin with.