It is a complicated one. Here in NM, for instance, it's *semi-legal in state law, but it may be outlawed by city/town/reservation or federal ordinance.
By semi-legal, I mean to say that you can't just dump gray water by any means available:
1. The gray water may not include water from a kitchen sink.
2. It can't be
sprinkled on a lawn.
3. It can't be used for commercial operations.
See what I mean?
Lynn