I am trying to find the source for a water leak in my car when it rains. The answer here should also be good for hard to find water leaks in a house.
Is there a material I can use which tells me the material got in contact with water in the past? I mean it changes color, or deforms or does something visible permanently even if it gets dry later? I want to know that some area got water before even if it's dry now. I want to know this after the fact. I hope I explained what I am trying to do and know.
(For those interested: I did run the hose over the car for a while and saw no leaks. I think it takes time and it's happening under the inside panels)