Both of the previous are great ideas. Also consider, if it is an older valve, that the main does not close completely, for a variety of possible reasons. We see that alot in older homes. You can confi ... read more
1) Fiberglass tubs are notorious for getting hairline cracks that usually open up when someone is standing in it with the water running.
2) Also it might be a leak from upstream (plumbing behind the w ... read more