What Causes Water Leakage in the Cabin?

[MacSarah]

Water leakage in the car cabin can be caused by the following reasons: 1. Failure to close the car windows during rainy days, or not confirming whether the windows are closed after exiting the vehicle, allowing rainwater to enter various parts of the car from the windows. Over time, water will drip from beneath the car cabin; 2. Drainage issues. After ruling out human factors, if water continues to drip from beneath the cabin, the car's drainage system should be checked. The car has four drainage outlets: the two front outlets are for the sunroof, and the two rear outlets are for the car's flowing drainage; 3. Long-term accumulation of debris blocking the drainage outlets, especially in vehicles with a sunroof, as the opening of the sunroof makes it easier for debris to accumulate and cause leaks.

[CooperRose]

Last time I encountered a case of water leakage during rainy days while repairing a car, I found that water leakage in the cabin is often related to seal failure. The most common issue is the aging and cracking of the windshield seal, which allows rainwater to seep into the area below the dashboard through the gaps. Another frequent problem is the clogging of the sunroof drainage holes; when leaves and mud block the pipes, accumulated water can pour from the ceiling into the A-pillar. Deformed door seals or clogged door drainage holes can also cause water to flow along the interior panels and under the floor mats. If you notice water leakage near the passenger-side floor mat, it's likely due to a detached or broken drain pipe from the air conditioning evaporator, allowing condensation to flow directly into the cabin. It's recommended to check these areas first and use bottled water to test if the drainage holes are clear.

[StJoy]

As a veteran car owner who has suffered from water leakage, I've identified the main culprits for water intrusion into the cabin. First, failed sealant around roof rack mounting holes allows rainwater to seep through screw holes into the headliner. Second, rusted and damaged body weld seams, especially subtle cracks in older cars' rocker panels that are hard to spot. Third, deteriorated tailgate wiring harness grommets that let car wash jets force water back along wiring into the cabin. Fourth, sunroof frame deformation compromising seals, turning heavy rain into an open faucet. When I found 2cm of standing water in my car, tracing revealed a broken firewall wiring grommet was channeling engine compartment water directly above the accelerator pedal.

[McJack]

As a frequent customer of car detailing shops, I've noticed that many water leaks are actually caused by improper aftermarket modifications. For example, when installing a rearview camera, if the wiring isn't done properly and the rubber gasket isn't sealed tightly, it can lead to trunk leaks. After drilling holes in door panels for audio system upgrades, if waterproofing measures aren't taken, rainwater can seep into the cabin. Some careless window film installers damage the door's waterproof membrane during application, causing water to enter when operating power windows. Poor-quality rain guards attached with double-sided tape can curl at the edges and actually channel water inside. And if you apply dark film on the roof, summer heat can accelerate the aging of sunroof seals, leading to leaks.