Answer: First, there is nothing in the Oregon Residential landlord-tenant law directly on point. Nor would I expected there to be, any more than a law prohibiting residents from intentionally defacing community property. It just goes without saying.
Looking for a remedial statute for recourse, however, is not difficult.
Check your community rules to see what they say. While I would not expect there to be a direct prohibition against wasting water, there very well be something that comes close to the point. If there is some provision in your rules that you can point to, then you could use a 30-day notice of termination under ORS 90.630.
However, I'm not sure you want to permit the resident 30 days to cure. Under these circumstances, you might want to resort to the non-curable 24-hour notice statute, ORS 90.396(1)(f), for outrageous conduct. While it is true that landlords and managers should not use the 24-hour notice if a 30-day curable notice would suffice. Accordingly, I would suggest that before resorting to the 24-hour statute, you "paper your file" by giving him a written warning notice, say seven days in advance, telling him what you will do if he does not stop. If he continues to flagrantly waste the community water, then file the 24 hour notice and let the judge decide. I suspect he or she will come down on your side of the issue.
Also, keep in mind that if you are forced to issue the 24-hour notice and go to court, at the first appearance, the court will encourage both parties to resolve the matter. In this situation, if the resident agrees to stop wasting water, then have him enter into a Stipulated Judgment of Restitution (which is prepared by the judge at the time of the first appearance), which would give you the ability to go back to court quickly (without having to file again), to evict should he violate the agreement.
There are other statutes that come into play here, although their violation would only give you a right to issue a 30-day curable notice of termination:
- ORS 90.740(3) (Tenant Obligations) provides that a tenant shall: "Behave, and require persons on the premises with the consent of the tenant to behave, in compliance with the rental agreement and with any laws or ordinances that relate to the tenant's behavior as a tenant."
While this provision requires you to look elsewhere (e.g. the rental agreement, laws, rules and ordinances), I suspect checking with your local water bureau, you will find certain water conservation rules and regulations that prohibit intentional waste of public water.
- ORS 90.740(4)(a) (Tenant obligations) also provides that a tenant shall: "Use the rented space and the facility common areas in a reasonable manner considering the purposes for which they were designed and intended;"
Again, this provision is not directly on point, I think we can agree that that intentional waste of water is not a "reasonable" use of the rented space. Moreover, ORS 90.130 (Obligation of good faith) helps out here, since it clarifies that "Every duty under this chapter and every act which must be performed as a condition precedent to the exercise of a right or remedy under this chapter imposes an obligation of good faith in its performance or enforcement."
 In briefly looking over the MHCO agreement I do not see language directly on point.