Oh, I solved the mystery of the running water. Someone, either the gardener or the pool guy, had left the hose on - unbelievable. It has one of those squirty things on the end so the water wasn't gushing out, but it had been left on at least several hours (if the gardener had done it, which is what I suspect, as I would have heard it the night before) and it was leaking from the spigot itself. I turned it off and all is well and well is all.