How to detect where water is coming from on external wall
I have used a flir camera to find leaks in roofs the water trails show up as cold areas and the thermal image even works to some extent through the wall. In 1 case the water was coming in more than 20' from the wall running down a rafter then down the wall I could not see it with my eyes but the camera made it quite easy to pinpoint. I use the camera for other things like finding bad electrical connections and leaks in ductwork so they can be a handy tool for a home owner there are quite a few models on the market for 200-400$ that work with some smart phones.