you can get an in-line gizmo which is part of the toilet flex SS water line which is supposed to shut off the water if it "observes" a leak. We have these, and they really work. We had a tiny, tiny leak in the crawl space with the downstairs 1/2 bath and that caused the water supply to the toilet to literally stop. Wasn't horrible under the house, and probably no more than 50-100 gallons until I got off my lazy butt and checked out things. The line is pretty cheap, around $15 bucks each.