My Son owns a twenty year old brick home. There is a continual leak on top of the foundation on the outside of the house.Located in the interior of that same wall is a shower. A plumber suggested that the drain pan may be the problem but my Son has not used the shower in the past twenty days. He did this deliberately to narrow down the source of the leak. Since there has been no water in the shower for so long could it be that there is a leak somewhere between the back side of the shower stall where the faucets and water pipes screw together? If so how can we get to it? The stall is heavy plastic(one peace). Any help with this would be deeply appreciated.
Thanks much.

To see if it's a leak on the shower vavle, take faceplates off vavle body and you should be able to look in at vavle body to see if its leaking. As far as gaining accest to the leak(if you find it is there) you will have to either cut into shower, remove shower, or remove brick siding. No easy fix here. Please let us know what you find, and we will try to point you in the right direction.

MGD77 has good point: since it still leaks - and nobody is using shower - than it is pressure leak and could be coming from h/c water supplies.

I would first remove shower faucet trim, too flash light and look inside the wall looking for wetness. However, you should be able to hear the leak. Do so and let us know what you've found out. Good Luck. Milo