What to do if you find water in your car

Found water in your car? We cover the common entry points -- sunroof drains, door membranes, rear lights -- and what to check first.

Know what you are looking for

The signs are usually obvious once you know them: mould on the seats or headlining, windows that steam up even when the car has been sitting overnight, a smell of damp or mildew that comes and goes with the weather. Less obvious ones include intermittent warning lights (airbag, central locking, ABS), electrical gremlins that come and go, and the sound of water sloshing somewhere under the trim when you corner. If you can hear it moving, there is a significant amount in there.

Before anything else: find the source and fix it. Drying the car without repairing the leak is a temporary measure at best.

Start with the boot

The boot floor is one of the lowest points in the car and the first place to check. Feel the carpet -- if it is wet or cold-damp, lift it. Mop up what you can with old bath towels. If the water is confined to the boot and the passenger carpets are dry, there is a reasonable chance you can dry it out, repair the leak, and be done with it. Check again after a few rainy days to confirm.

One thing to be aware of: some cars have the battery in the boot. We have seen a submerged battery burn out an entire wiring loom. If there is standing water near the battery, disconnect it before you do anything else.

Wet carpets: how to deal with them

If the passenger footwells are wet, the seats will need to come out -- in most cars both fronts, though in smaller cars sometimes just the one on the affected side. Lift the carpet, then use a wet-vac to suck the water out. Do it several times over a couple of hours; the foam underlay holds a surprising amount. If only one side is wet, you can sometimes just lift the carpet on that side and hook a bungee strap to the grab handle to hold it up while you work.

Then the car needs to dry properly. A plug-in fan heater -- firmly secured, not sitting in a puddle -- aimed at the wet area with the windows open about an inch. On thick foam underlay this typically takes two to three days; thinner foam in a smaller car, sometimes just one. If both sides are wet, work on each in turn without necessarily removing the centre console.

If you are not certain it is fully dry, leave it another day. Water left under the carpet causes rust, smell, and electrical problems that cost far more to fix than the original leak.

Electrics, airbags and seats

Removing and refitting a seat with the ignition off means the car often will not register the disturbance -- so you may avoid triggering the airbag warning light. Most seats have a plug underneath that needs disconnecting before the seat will come free.

If the ignition was on during any of this, the airbag module may need resetting. A garage can do it; there are also diagnostic tools available, though most of the cheap ones do not do what they claim. We use a unit made by Foxwell.

On the question of whether to drive the car: if your radio is playing up, you might judge that low-risk. If the ABS light is on, do not drive it. And do not leave it sitting for too long in a wet state either -- a week or two and mould becomes a second problem on top of the first.

Mould is a health issue, not just a smell

If the car smells of stale water or mildew, take it seriously. Mould spores in the enclosed space of a car can reach concentrations high enough to cause real health problems: flu-like symptoms, sinus issues, fatigue. Over the years we have spoken to quite a few people who were too ill to drive their cars in and had not made the connection. One customer was off work for two weeks, returned to her car, and was ill again for another two weeks before she worked out why.

Do not put a car cover over a car that still has water in it. A cover traps moisture, and condensation spreads everywhere. Mould thrives in darkness, warmth and dampness -- a sealed car cover provides all three. A garage or carport is better; bath towels to absorb what you can in the meantime.

Finding the source yourself

If water is only dripping from a high point and has not reached the carpets, a bucket with towels underneath will manage it until the repair is done. But do not assume the one drip is the only source. We regularly find cars where it is dripping from the sun visor but also running silently down the A-pillar into the footwell.

If you want to investigate yourself, be careful not to destroy the evidence. If you think the rear lights might be leaking, do not pull them off, clean everything up and refit them before you have confirmed it -- you may accidentally fix it and lose the trail. Instead, get someone in the boot with a torch while you run a hosepipe over the outside of the light. If it is leaking, you will see it. Then check both lights and the surrounding grommets; if one seal has gone, the others are likely the same age.

For specific makes and models, our video archive of water leaks we have found and fixed is a useful reference. We have also written up our diagnostic process in more detail if you want to understand how a professional leak trace works.

After the repair

Check the car again after it has rained. It is common to repair one leak and find water appearing at the same low point from a second source that was there all along. The lowest points are typically the front footwells, the boot floor, and occasionally the door pockets.

And if you are using a local garage: be patient with them. Water leaks can be genuinely difficult to trace, and a methodical job takes time. We have seen the results of rushed work -- a large hybrid Audi came in where someone had run bath sealant along the outside of the rear window. On a car worth between £20,000 and £50,000. Hybrids and full electrics carry high-voltage systems throughout the car; water and those systems do not mix.

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