Pinhole leak in a water supply pipe in the basement.
Luckily I went down to the basement just before 9:30 to admire all of the clear floor space that my hard work had accomplished, and to plan the next mode of attack. The relevant phrase here is "what's that noise?" "What's that noise" NEVER ends well. Naturally, the leak was over a section of basement that is full of unsorted stuff. I don't *think* we actually lost anything. The top edges of one of the boxes of albums got wet, but the bottoms of the boxes hadn't soaked through yet. No problem there. A lot of the other stuff was either in plastic or dryable fabric. Bob turned off the water, I started up the wet/dry vac, and we went for our all-purpose solution to all problems house:
we called dad.
We have drained the house water down to the first floor, and the remaining water in the pipes is dribbling out through the pinhole. That takes a while. We have determined that we have copper pipe, but it's too small. We have hose clamps that are too large, hose clamps that are too small, and a couple that might work. I'm not sure I'm getting a shower tonight, but Bob is doing his best.
On the bright side, at least I had an urge to go down there. If that had gone for all day and evening tomorrow...