Good Evening Jeff,
That's kind of what I had figured... I'm building the dark room mainly for myself and don't really mind sharing, especially if doing so will offset some of the cost of the build-out. I have the spare space in the back of my shop so it's paid for whether I end up with anyone who wants to rent time there or not.
Talk about not being usable for 6 months out of the year... My tap water is 80+ right now (after cooling down for about five minutes). Never had that issue up in Kansas. Of course we buried our water lines more than a foot underground to prevent freezing so they stayed cooler in the summer as well. Luckily I've got several chillers lying around with nothing to do so I'm sure I'll end up retrofitting one of those into the darkroom, at least to temper the Jobo water bath.