When we built our NM house, 1999, I tried to fix the plumbing so that the shower water would dump into the yard and irrigate the trees. The county inspector said "no" so we plumbed that water into the sewer. Then a few years later, the state revised the Environmental Laws to allow, even encourage, "gray" water recycling for irrigation. A settling tank is required IIRC but they clearly established the intent that "gray" water could be used locally for irrigation. Now new houses have the option of two plumbing systems one for gray water discharge locally and one for black discharge into an approved sewage treatment system. I guess RV parks could, if they chose to do so, do the same. I doubt that RVs have the same options, but I don't know. It doesn't bother me for a second to dump gray water at home, the plants appreciate it, but then we have several acres of land to buffer the drainage. ???