Have you ever wondered what happens with your water once it makes its brief passage through your house?  Not the water that resides in your toilet, but the water that you shower or wash dishes with.  Water that is not potable, but also not heavily contaminated with chemicals or your bodily waste (ewww).  Couldn't this water still be used for certain functions like garden watering or heading back to the toilet (as long as you don't let your dog drink out of it)?