Proving it can be done! And it has to be cheaper long term. You'd think with all the world and trying to be green and saving the environment and saving money we'd have done this a long time ago.
I don't believe it's being done on a small scale as much though. I used to work on a campus that had a closed water system, all water was filtered and reused. It was a large scale operation though, nothing that would work for a house.