It can be easy to miss, but water leaking into your car can cause serious issues if left to worsen. Thankfully there are some telltale signs to identify when you have rainwater leaking into your car interior, and some common causes that can help identify the cause.  

6 Signs of water leaking into your car 

If you notice any of these signs, it’s wise to investigate fully to find the cause of the leak, before it causes irreparable or expensive damage. 

1. Wet floor mats 

An unmistakable sign that water is entering your car is if the floor mats are sodden, which is likely to be especially noticeable after heavy rain or a period of not driving the vehicle.  

It's likely if the floor mats are wet, then the carpet too will be soaked through, the extent of which can help identify where the leak has originated from. 

2. Discoloured Upholstery 

When water leaks in through seals, it is likely to also bring some road grime, dust and dirt. If this water soaks into your upholstery, be that the seats, carpet or headliner, it is likely to leave a discolouration.  

Usually an off-white or light brown colour, discoloured fabric is an easy way to identify where the water is entering, marks on the headliner are likely to be from a leaky sunroof, for example.  

3.  Window misting or screen freezing on the inside 

Excess moisture inside a vehicle will present itself in a couple of ways, if it's particularly cold outside the vapour may condense on the inside of the windscreen and freeze. Alternatively, it can simply fog up the windows, requiring wiping or airing to remove.  

If your windows constantly fog up, check for other signs of leaking. Usually, the windows will fog nearer the source first, for instance, a broken boot seal will cause the rear window to fog most.

4. Musty or mouldy smell 

One of the most common causes of a smelly car interior is an old water leak that has not been addressed, or at least the upholstery is not sufficiently dried out. 

To remedy a mouldy-smelling interior, with no obvious leak, thoroughly clean the carpets and floor mats. Once clean and dried, monitor closely the carpets around the problem areas for dampness, especially after rain. 

5. Electrical faults 

If you’re experiencing strange electrical faults with no apparent cause, ruling out a water leak is a good step. Problems usually occur in cars that have the ECU located in or around footwells and by door frames.  

This is one of the most unfortunate ways to find out you have a water leak, as it may be too late to save the damaged components if the faults are caused by water damage. Check with an auto electrician if the faults persist. 

6. Sloshing noise inside the car 

A noise similar to water moving around in a half-full water bottle is often caused by water getting into your doors.  

Water entering the door frames is not actually uncommon, the seals on the outside are not designed to prevent all water ingress. Instead, the doors have drain holes to allow the water to simply drain away. 

If these drain holes become clogged, the water can build up, potentially leaking into the car, causing problems with electric windows and speakers, or causing the door itself to rust. 

Why Your Car Is Leaking 

Water leaks can be difficult to trace, but there are only a certain amount of entry points on most cars.  

Common causes for water leaks include: 

• Broken or missing door seals 
• Perished or shrunken rubber seals 
• Perished seals around sunroofs 
• Missing trim pieces - water can leak through the holes in the bodywork 
• Broken or torn convertible roofs 

Who can fix a water leak in my car? 

Whilst there aren’t likely to be any specialist damp/leak experts for cars, any general mechanic should be able to investigate water leaks in your car.  

If possible, we’d suggest a garage that specialises in your make of car, as they are more likely to have come across the common causes on that specific model before.  

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Cost of car water leak repair 

The cost to fix water leaks can be anywhere from £50 to £2,000+, depending on the level of damage caused by the water before it is fixed. 

Some water leaks can be fixed simply by replacing a broken seal or rubber, some may even still be present but have simply become dislodged from their intended position. Both situations would be reasonably cheap to fix.  

If there has been rainwater leaking into the car for a while, costs could quickly rise if electrical systems have been damaged, or upholstery needs to be professionally cleaned or replaced.  

What damage can a water leak cause? 

If you have a water leak and are wondering whether to bother getting it sorted, we would recommend doing so as soon as possible, purely to avoid hefty bills down the road. Water damage can be significant. 

Damaged ECU 

The ECU controls every electrical system in a car, and the module is sometimes mounted near potential water ingress points. 

The cost of repairing water damage to your car's ECU could easily run into the thousands, as a replacement often involves also replacing ignition key modules, immobiliser modules, door locks and more.

Mould and ruined upholstery 

If water leaks are left unabated, mould is likely to develop, this combined with staining, carpets and seats can be damaged to the point of being uneconomical to repair.  

As they’re not a service item, replacement carpets and seats can be hard to come by, and take many hours to replace. 

Rust 

Water causes steel to rust, and whereas modern cars are protected from this by design (as well as their paint), water-logged carpets and upholstery can cause untimely corrosion to areas such as floor pans, bulkheads and roof panels. 

How to fix a water leak in your car 

We’ve explained why it's critical to fix a water leak, and how to spot one, but how do you fix a water leak in your car? The answer generally depends on where the leak is from. 

Once located, assess the area from where the water is leaking, if a seal is obviously damaged or not properly secured, try to reattach or affix this. When investigating a leak, check for any loose bolts, screws or trim panels, as these could be preventing a seal where required.  

If the leak is not easily apparent, or you need to remove panels or components for better access, we’d advise seeking professional advice first.  

Temporary solution for a water leak 

Whilst a short-term solution may not be perfect, it could help prevent further damage, as long as it doesn't become an insufficient long-term fix.  

Plastic bags or sheeting can be used to stop water ingress, or if the area of the leak is not known exactly, a car cover could be used to shield the affected area during a shower. Half covers are also available that just cover the roof and windows.  

We would not suggest using silicone sealant or glue as these can sometimes make the problem more difficult to fix permanently later on.  

Speak to the experts 

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Author - Joseph Law

Joseph has been writing about cars for over seven years and writing for Bumper for over two, blending his passion for automobiles with a talent for storytelling.

Joseph has written about engineering and cars for Autozilla, Komaspec, and several engineering manufacturers. When he's not writing or tinkering with one of his five cars, Joseph dreams of owning an Alfa Romeo 33 Stradale.