[Setec Astronomy]

Originally Posted by admac

some people re-use the gray water for non-potable purposes like watering the lawn or landscaping. it's a conservation effort.

I'm familiar with the technique, having lived through two periods of water rationing. I'm just not familiar with building a house with two sets of drain plumbing to facilitate that or to relieve the load on a septic system (in which the aforementioned "draining it under the back yard" would not be considered a conservation method).