We must retrofit our existing homes to include neighborhood treatment and reuse of community water and sewer. The expense of converting an existing drain system for recycling grey water is prohibitive. Maybe if you were remodeling your bathrooms, the extra cost might be worth it.
We could feasibly install a community recycling system for an HOA or city building or golf course. Take a look at this San Francisco-based company Epic Clean Technologies
They can recycle 95% of all the site water usage. They only take up 3 parking spaces with their equipment. All residents could then share the cost.