Saving our kitchen sink water in a bucket and watering plants with it, we are amazed at how much water we use. I am sure this is typical of most households. Instead of the government paying people to abandon their beautiful lawns for dirt, why not do the following.
Replumb houses with inexpensive PVC pipe to have separate grey water drains leading to an outside storage tank for irrigation. For all grey water drains, connect the drain pipe to the new line just before it enters the 4-inch black water line and capoff where it entered the black water line. This is nothing like replumbing a house because this is all zero-pressure gravity-flow line, so leaks are easily prevented by just gluing the PVC properly. Moreover, nothing is touched in the house drainage network upstream of the existing black water pipe.
I wonder why the water companies and government agencies have not already been doing this big time. So simple and cost effective.
By the way, I am not proposing breaking into concrete slabs to do this; this is proposed only for easily accessible connections as in raised floors. If soaps and detergents are a problem for landscaping, then filters and/or settling tanks before irrigation can solve that.