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)

  • I can think of a bunch of household materials that could be used in this capacity, though which to use would depend on where/how exactly this material would be applied. A bit more info on your specific situation could help – mac Nov 29 '12 at 21:21
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    Somewhere I have instructions for making a powder that bursts into flame when exposed to water. Probably not what you're looking for, though. – Brian White Nov 29 '12 at 22:08

What you're looking for is called "water contact indicator tape". It's used in cellphones and other electronics to detect when damage was caused by water for warranty-rejection purposes. You get it wet, and it turns bright red, as shown on page 2, and stays that way permanently.

Though it's generally only sold by the 100-count reel.


Depending on how much water you're dealing with, newspaper or a paper towel can be an easy low tech solution. I would check a paper towel fairly often since a little water will quickly soak the entire thing.

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    This is one of the solutions I was thinking of. Drawing some lines on a piece of paper using a pen with water-based ink might be more sensitive than newspaper (I dont think the ink is water soluble) and more permanent than paper towel (once wet now dry might be hard to detect) – mac Nov 29 '12 at 22:11

Blue paper shop towels turn darker blue and are quite obvious when wet. They sometimes retain a different color or stiffness once they dry out, so they are mildly indicative once dried and highly indicative while whet.


One of the simplest leak detectors is a stethoscope. Open the hood. Turn the key to the "on" position. Turn the fan on High. Close the doors. Move the stethoscope around the windshield, door openings, sunroof etc. With the fan running the cabin will become slightly pressurized and the air will escape at the point of the leak. The air will generate a noise that is audible with the stethoscope.

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