We were just getting to bed and the cat was standing in front of the hall closet where the water heater is, meowing. There was just a tiny bit of water peeking out from under the door, but that triggered him. If we'd not seen it before going to bed there would have been water everywhere this morning. Last night though it as easy to contain and re-direct down the drain. The water was running out the side access panel and most of it wasn't making it to the drain.Those things have a sentient aspect. They just know when to fail.
How did your cat alert you?