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How To Diagnose A Water Leak On Your Car


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Just Know That The Most Important Tool To Fix And Diagnose A Water Leak Is Patience.

Diagnosing most problems in modern cars is made easier through the use of schematics (like wiring diagrams) and tools (like the FIXD sensor and app), but interior water leaks can be far more difficult to diagnose and repair. A water leak can be caused by a number of problems ranging from bad weather-stripping to misaligned components to rotting leaves, so tracking down the source of the leak is usually much harder than the fix itself. And that’s what I encountered recently when my wife’s Ford Escape developed a massive puddle on the driver’s side floorboard. 

water-soaked carpet

Chasing a water leak can be a huge headache, but here are some helpful tips for diagnosing – and, more importantly, repairing – a water leak on your car.

What To Know About Water Leaks?

Unlike a fluid leaking from an engine, tracing the source of a water leak is more difficult because there’s so much more stuff in the way… like the entire interior of the car! To make the diagnosis even more of a challenge, water will always flow to the lowest point, so just because water is in one area, it doesn’t mean it’s coming from that same area. 

vehicle with carpet removed

This is why it’s important to note how a vehicle is parked when the water leak is detected (on a hill, leaning to one side, etc), which helped me narrow down the location of the leak on my wife’s car: she parked in a parking lot on a moderate slope, and the leak was at its worse when she parked in a particular area where the driver’s side was pointed downhill.

Tools/Materials You Might Need

The good news when it comes to diagnosing and repairing water leaks is that you generally won’t require any specialty tools. To diagnose the water leak on my wife’s car, I removed the trim pieces along the floor on the driver’s side, the left side A-pillar, and the sun visor; the only tool I needed for all of this was a Phillips head screwdriver. Of course, you’ll need a source of water for testing purposes and you can also purchase a leak detection spray (an aerosol spray that drives to a chalky finish to better trace water).

view of sunroof drain with a-pillar trim removed

Repairing the leak only took an air compressor to blow air through the drain lines, but removing the seats and center console to take out and dry the carpet did require some added sockets and torx bits, but nothing you can’t get at your local home improvement store. A ShopVac and a box fan will help with clean up, and for good measure, hang a DampRid in your car to help remove remaining moisture from the air.

How To Diagnose A Water Leak?

top view of sunroof with clogged drain

Whether you see water running on the inside of a window or you notice a puddle on the floor, almost all water leaks are different and few are as straightforward to diagnose and repair like replacing a serpentine belt or changing manual transmission fluid. In the area where the water has accumulated the most, try to pull back the carpet as much as possible and/or remove interior trim such as A-pillar, kick panels, etc. This will help make the water leak more obvious during a water test. For the water test, use moderate water pressure such as a garden hose and don’t use a pressure washer or a drive-through car wash, and try to have a second person so one person can spray and the other person can look for leaks. When spraying the car, start down low in the area you’re focusing on and go slowly to help best pinpoint the location of where the water is getting into the car.

clogged sunroof drain

In the case of my wife’s water leak, the problem ended up being leaves and other small debris in one of the drain tubes for the sunroof. These tubes let the water run from the sunroof down the A-pillar and then out the wheel well, but with the clog, the water was overflowing and then pouring into the headliner, running down the A-pillar and then puddling up in the driver’s footwell. As I said earlier, the repair was simple and only took about a minute since all I had to do was to clean out the tube, but chasing the leak and drying out the interior took about two days in total. Because the carpet and padding were soaking wet, I took the seats and center console out of the vehicle in order to remove the carpet and dry it in the sun to prevent any mold or floor pan rust.

top view of the sunroof drain once cleared


Water on the inside of a car can lead to major problems down the road, so you’ll want to be sure to address any leaks as soon as possible. Waiting too long can lead to expensive damage to your car’s wiring and body parts and if mold is present, it could lead to health problems for passengers. The good news is that with a little patience, repairing a water leak yourself will save you a lot of money versus letting a ship diagnose the water leak for you. 

Jeffrey N. Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a ’91 GMC Syclone. #GirlDad #SaveTheManuals

We’re here to help you simplify car care and save, so this post may contain affiliate links to help you do just that. If you click on a link and take action, we may earn a commission. However, the analysis and opinions expressed are our own.

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About the Author

Jeffrey N. Ross

Jeffrey N. Ross

Lifelong automotive enthusiast with a soft spot for offroading. Wrencher turned writer, but I still love to tinker on just about anything with an engine. Dream car: tie between a ‘71 Hemi ‘Cuda and a '91 GMC Syclone. #GirlDad #SaveTheManuals

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