Water Leaking into Your Car? – The Causes and How to Fix It!

A breach in our vehicle is usually something that shouldn’t be taken lightly. Puddles of oil, coolant or fuel can all signal something potentially serious.

The only advantage to these sorts of leaks is you can easily identify the liquid. Each of the three so-called lifeblood fluids is distinct in color and smell. That helps you narrow down where the problem could be located (e.g., oil reservoir).

But what about plain old water inside your cabin?

Despite not being toxic or harmful, water leaking in your car is still a sign of an issue, and can even cause further damage.

Side view of silver car driving in heavy rain

Wet patches on your upholstery or carpeting can be frustrating to dry and can leave stains. That’s not to mention an unpleasant smell that can develop over time.

And it could be more challenging to find where it’s coming from than you may expect.

In this article, we’ll share with you everything there is to know about water leaking in cars.

We’ve listed the steps you should take to determine the source. You’ll find out all the possible causes and repair solutions for each one.

We’ll also guide you through what to do once you’ve pinned down the source of the issue, to get the problem fixed.

Diagnosing Water Leaking in Your Car—When Does it Leak?

Successful diagnosis requires two steps.

Firstly, short-list the symptoms your car is experiencing. In this case, it’s pretty simple. You’re finding puddles or damp patches inside your vehicle.

Secondly, take notice of when the unusual symptom crops up. This will help you narrow down the source of the leak in your car.

Water can move around in surprising ways inside your cabin. You may find wetness a long distance away from the breach itself. Instead of having to go over everything with a fine-tooth comb, you can check specific parts.

Depending on the current situation, you may find the cause of a leak completely different. Let’s take a look at these in turn…

When Raining?

Puddles in your cabin after rainfall could have quite a few causes. Before you begin a full inspection, make sure you haven’t left anything open.

A window that’s left cracked open, even slightly, can let in a substantial amount of rain. If everything looks sealed up tight, you’ll have to start checking around.

What Could it Be?

Are rainy days hitting the inside of your car just as hard as the outside? It could be one of these parts at fault:

  • Sunroof drain.
  • Door membrane.
  • Door weather stripping.
  • Windshield rubber.
  • Window seal.
  • Cabin air filter.

Inspect each of these areas for signs of damage, and moistness on the inside as a sign of water ingress at these points. If you find anything that looks perished or damaged, it’s the likely culprit, and you can then move on to a repair it.

When Parked on a Slope?

You might have figured out the leak gets worse or only appears when you park on an incline. If you suspect this happens, but you aren’t sure, test it out.

Find a slope or a steep hill and park your car there for 15–30 minutes. See if the mystery breach acts up or not.

What Could it Be?

The good news is there won’t be as many parts to check here. The fault is most likely within your sunroof.

In a Car Wash?

The purpose of going through a car wash can start to seem futile with a leak. A sopping wet interior can take away the joys of having a gleaming exterior.

Don’t forget to verify that you didn’t accidentally leave a window or sunroof partially open.

What Could it Be?

As with rainfall, there are a number of components that could be affected. Review our sections below about the following:

  • Sunroof.
  • Door seals.
  • Door weather stripping.
  • Windshield rubber.
  • Window seal.
  • Cabin air filter.

When the AC is Running?

Cool air shouldn’t come at the cost of unwanted moisture. Those of you living in hot climates may have to sacrifice comfort for a short period to test this theory out.

Attempt to drive around without your AC running for a while. Keep an eye on the places where water accumulates. If you notice improvement, you’re one step closer to solving and fixing the breach.

What Could it Be?

Dampness, drips or puddles inside your cabin when you’re using the AC could mean there’s a problem in one of these:

  • Air conditioning system.
  • Heater core.

Windshield Replacement

Professionals can make mistakes every so often. If you’ve recently had a new front or rear windshield installed, it may have been poorly fitted.

Wet patches collecting towards the front or rear of your cabin could warn of shoddy installation, so it’s worth checking this out.

What Happens if You Ignore a Leak?

Water isn’t a hazardous substance in itself. Having said that, an untended leak can increase the risk of unpleasant scenarios such as the below.

Mold Growth

Moisture can breed mold no matter where it is if not dried up, and this can wreak havoc with some peoples health.

This applies to those of you with existing allergies or weak immune systems. You might end up with bouts of throat irritation, nasal stuffiness, and more.

Attractive Environment for Pests

Leaving your vehicle unused for long periods with an uncontrolled breach is unwise. Pests like rats will appreciate the readily available water to drink from.

Upholstery and Carpet Damage

Even resistant materials like vinyl can succumb to never-ending moisture.

If the liquid is dirty or contaminated, it could result in permanent stains. This could decrease the overall value of your vehicle if you decide to sell it.

Nasty Smell

The odor of mildew can be foul, much like the smell of an old wet towel.

Don’t let it get to the point where you have to hold your nose whenever you enter the vehicle.

Possible Causes of Leaks – and How to Fix Them

You now have an idea of when the leaks happen and what to take a look at.

Next up, you’ll learn how and why each component could be malfunctioning. We’ve included brief guidelines on how to check and fix each of them.

Vehicle Sunroof

Sunroofs are a lot more penetrable than you may have thought. They do a good job at keeping out solid debris but are less adept at preventing water leaking into your car.

In fact, the roof is built to leak, albeit in a controlled fashion. They’re equipped with drainage tubes that carry excess water from the roof, down and then off your vehicle.

The drain tube holes are usually located underneath the sunroof itself. If you open it all the way, you should be able to see them.

If the tubes become clogged, fluid will drain through the sunroof rather than away from it. It could drip down your roof to your dome light, front seats or carpeting.

This is why parking on a slope at the wrong angle could make it worse. Overflow won’t have the chance to travel down the blocked tubes. Instead, it will seep into your cabin straight away.

What’s Going on: How to Perform an Inspection

Find the entrances and exits to your drainage tubes. The holes are usually located underneath the roof itself. If you open it all the way, you should be able to see them.

Exit portals might be in the driver’s side door jamb or somewhere underneath your vehicle. This information can be found in your car’s owner manual.

Slowly pour a small quantity of water into each drain hole. Monitor the exit holes to see how quickly the liquid flows out. If it takes a long time, you’re likely dealing with a

blockage.

How Can You Fix it?

You can use an air compressor to clear out whatever is clogging the tube. You may also have to get a flexible wire for thorough cleaning if there’s a lot of dirt.

Door Seals / Door Membrane

Every door in your car contains a membrane. This sheet is made of lightweight, durable materials, such as polythene or foam.

Automotive doors aren’t airtight, meaning water can seep into them. The membrane protects the inner upholstered part from getting wet.

Water runs down the protective sheet and out of holes built into the bottom of the door. If the membrane tears or grows thin with age, it won’t be as effective.

If this happens, you’ll usually find damp spots on your carpeting, in the footwells. The moisture will collect there instead of being guided out of your door.

What’s Going on: How to Perform an Inspection

Remove your door panel to check the membrane. If you see any perforations, you’ve found where your leak is coming from.

How Can You Fix it?

You can try a temporary fix with tape, but it’s preferable to have the whole piece replaced.

Door Weather Stripping

The weatherstripping is the rubber seals that surround your doors. If the rubber is brittle, aged or damaged, it can allow too much water into the door.

Even with a secure membrane, the liquid can overflow from the door into your vehicle. These leaks usually cause pools or dampness right next to the door, by the footwells.

What’s Going on: How to Perform an Inspection

Visually inspecting the seals will tell you all you need to know. Roll your window up and down to see if the rubber is pressed firmly against the glass. If not, a replacement might be in order.

A telltale whistling noise while you’re driving can also suggest old weather stripping. Air will pass through the worn rubber into your cabin, creating the whistling noise.

How Can You Fix it?

Minor wear and tear can be repaired with restorative products for rubber. If the seals are in tatters, you’ll need to replace them with new ones.

This video shows you how to fix the weatherstripping at home:

Windshield Rubber

Both your front and rear windshields are fitted with rubber. These rubber seals hold the large panes of glass securely in place.

They’re supposed to be a perfect fit. If the windshield wasn’t installed correctly, gaps or crevices could exist between the glass and the rubber. Gaps can also occur if the rubber wears down with age, although this is less common.

Rear windshield leaks are easier to identify. You’ll find dampness in and around the back of your vehicle.

If it’s your front windshield, the liquid could collect in various places. It may drip down your dashboard towards your radio, or pool in your footwells.

What’s Going on: How to Perform an Inspection

We mentioned this earlier. If you’ve recently had either windshield replaced, it may have been done incorrectly.

You might also hear air whistling into the cabin when you’re driving.

How Can You Fix it?

The glass will have to be taken out and refitted properly. The old seals have to be replaced if they’re distorted or damaged.

Window Seal

Each window has rubber fitted against it on either side. When you roll your windows up and down, the glass is pressed between these two seals.

Both seals should be flush against the glass on either side. External conditions, such as extreme cold and exposure to sunlight, cause the rubber to lose its flexibility with time.

What’s Going on: How to Perform an Inspection

Carefully examine the rubber seal around your window. If it’s brittle, inflexible or missing pieces, it’s done for.

How Can You Fix it?

You could try a restorative product first to see if that makes a difference. If that fails, install new seals or have a mechanic do the job for you.

Air Conditioning

The AC in your vehicle has a built-in drainage pan to catch the overflow. The extra condensation travels to the pan and is then expelled from underneath your vehicle.

If the drain pan or tube, or both, are dirty, fluid could be forced into your cabin. Water will come from your vents, or you may see dampness on the dashboard. If there’s a lot of back-flow, your carpets could get wet too.

What’s Going on: How to Perform an Inspection

If your car stays dry when you avoid using the AC, you’ll know for sure.

Newer automobiles can include sensors to warn you of a blockage in the system. If yours has lit up and you have a leak, the guessing game is over.

For older cars, you’ll have to take a peek at your drain pan and pipe. Consult your vehicle’s owner manual to find out where it is. Debris in the pan could have come from the tube.

How Can You Fix it?

If you feel up to it, you can unclog the drain line at home. Use a slim bristle brush and wet-dry vacuum to clear it out. Make sure to remove any solid muck from the drain pan too.

Otherwise, head to your mechanic. Maintaining your air conditioning system on a regular basis is essential to keep it operating smoothly anyway.

Heater Core

The heater core is not to be confused with the radiator core. It is responsible for all the heat-related airflow inside your cabin.

It uses coolant to avoid overheating while it heats the air blowing into the vehicle. If one of the tubes that circulate coolant grows loose or damaged, a leak could occur.

What’s Going on: How to Perform an Inspection

Carefully sniff the damp areas in your car. If you can detect a sweet smell, you’re dealing with a coolant mix, which can only come from a leaking heater core.

Under no circumstances should you taste-test to see if it’s pure water or not. Antifreeze can be poisonous, even in the smallest quantities.

The leak may also be accompanied by foggy windows and erratic heating functions. Note that inhaling vapors contaminated by antifreeze can be dangerous too.

How Can You Fix it?

You’ll want to get this repaired as quickly as you can. Either the hoses or the entire heater core will have to be replaced if it’s corroded or malfunctioning.

Accessing the unit can be tricky as this component is hard to reach in certain vehicles.

Your dashboard may have to be taken apart first. In other cars, the heater core can be reached without much of a hassle, through the hood.

Cabin Air Filter

The cabin air filter is what shields you and your passengers from air pollution. The filtration material can capture everything from toxic emissions to pollen and dust.

A broken filter or careless installation could lead to a leak in your car. Rainwater can seep through the cracks and get into your vehicle.

What’s Going on: How to Perform an Inspection

Locate and examine the filter. Check your owner’s manual to learn where it is. In the majority of cars, you’ll be able to reach it without much trouble.

Inspect the filter to see if it’s fitted right and free of cracks or tears. Open and close the lid over it to make sure it catches and stays shut.

How Can You Fix it?

Cabin air filters aren’t that expensive. If yours is damaged, throw it out and buy a new one. Those of you with badly-fitting units, double-check your car’s specifications before buying a replacement.

A broken lid may pose more of a challenge. You’ll want to repair whatever mechanism is preventing it from closing. You can also try a temporary DIY fix like taping it shut.

After Finding the Leak

You’ve successfully found out what’s causing the leak. All you’ll have to do is fix it and get your vehicle dry again.

Take Appropriate Steps to Repair the Leak

We’ve briefly explained repair solutions for each issue. Make it a priority to address the faulty or dirty component to plug up the leak.

Dry Your Car

Once the fix is complete, you need to dry your car thoroughly. If the heater core was the culprit, you’ll have to wash the interior too. You don’t want coolant residue anywhere inside your cabin.

To dry out the cabin, use either a desiccant product or a dehumidifier. This is a necessary precaution to discourage mold, mice, stains, and nasty odors.

Your cabin shouldn’t smell musty, like an old, wet towel.

Final Thoughts

Water leaking in your car can range from a serious issue, such as a heater core problem, or something mild. If you’re lucky, it’s something simple to fix, like a loose cabin air filter.

You’ll never know unless you investigate. Don’t wait and see if the breach will miraculously disappear if you pretend it isn’t there.

By now, you already know that it won’t go away on its own. Intervention is needed. For the sake of your upholstery, resale value and your nose, you should act fast. Delaying the fix could lead to bigger, costlier automotive troubles in the long-term.

Do you have any questions for us or stories to share about your experience with water leaks? Don’t hesitate to leave us a comment below. We’ll get back to each and every one of you!

Shawn Furman

I've had a passion for cars since 8 years old, and been a subscriber to Auto Week magazine since my 10th birthday. Ever since I turned old enough to drive, I have driven as many vehicles as possible, while teaching myself how to perform maintenance and upgrade work on every vehicle I've owned. For the past 10 years, I've been honing my skills as a vehicle hobbyist, in recent years also enjoying writing car reviews, opinion articles, vehicle how-tos, car-buying guides, and even provide individual consultations for those who need car-buying advice. In addition to writing for Vehicle Scene, I currently write for Autolist, and also own and operate my own vehicle blog website, The Unlimited Driver.

Leave a Comment