Is Water Leaking Inside Your Car? Wet Carpet Diagnosis

Have you noticed your car’s carpet is soaked? Maybe one of the footwells is worryingly wet. Here’s how to diagnose where it’s coming from and what to do next!

Our example here is a BMW F10 5 Series – the CAT N car we looked at a bit over a year ago – complete with an absolutely drenched rear left footwell and wet door card. So, what are we looking for? Well in short: where did the water come from? Was it from an internal source like a spilled water bottle – or worse sugary drink bottle – or even worse, one of your passengers? It could also come from something like the AC vents if you have a evaporator leak. The former set of options should be pretty easy to work out. Is there an empty bottle rolling around in the area? Is the fluid contained to a single area like our BMW – just a single footwell? If the answer to those is yes, you can also verify it’s just water by giving it a sniff. If it smells sweet, or like wee, you’ll likely need to get the whole carpet out the car and either thoroughly cleaned or outright replaced. If it just smells like damp carpet, dry it out with towels and even a hairdryer and call it a day.

If you don’t see an obvious internal source, it’s time to start checking around the area to see if you can find any traces for where the water is dripping down. Feel the vertical carpet around the wet area and see if you can find any other water source. In our case while we didn’t find anything on the carpet, we did find that the bottom edge of the rear passengers door car was wet and crumbling. That was enough for us to start taking the door car off. You don’t need many tools for this, just a set of trim tools which really aren’t expensive, but it is always a faff. Still once we got it off we could inspect the damage to the chipboard backing – enough to rip one of the clips clean off – but interestingly it didn’t look like it was wet save for literally just the lower edge.

It’s worth checking your door seals too, that doesn’t require any disassembly and what you are hoping to see if soft, supple rubber free from tears and cracks. It should have some spring to it, rather than feeling like a flat solid block. In our case we did have a small tear, but we are pretty confident that isn’t our issue. If your car has a sunroof, definitely check the headlining area over the leak. If it’s coming from there the roof should still be damp too.

The final area to check then is the vapour barrier on the inner door. On our car this wasn’t attached overly well in a number of places so we suspect that was the cause. Luckily, this is pretty easy to remedy. A hairdryer on high or heatgun on its low setting will reactivate the glue and let you stick it back down. After that, make sure to remove as much of the dampness as you can get. We used tea towels to soak up the majority then the hairdryer to get it dry.