Ah, ok. I think I see the confusion. I think you're applying a false dichotomy here. It's not an "either you are clean or you don't get housing" in most places. But, if a therapist sees that addiction is a contributing factor, they will often make the free housing contingent on being part of a drug rehab program. So it's not "clean or else you're back on the street" but it's looking at it as part of the overall problem that's keeping a person from being self-sufficient. They aren't even generally piss tested as part of that. The cases where they are forced to be clean prior is when they are referred to housing services by a probation or parole officer. But that "remain clean" condition is more a function of the probation/parole than the housing program.