Car air con leaking water: puddle under the car or a wet footwell?

Water from the air con can be perfectly normal, or a sign that something is blocked. The difference is where the water ends up: under the car or inside it. Here you can read how to tell the two apart, what causes it and what you can do yourself.

By the team at Autobedrijf Willemsbrug, RDW-approved APK (MOT) test station since 1979 · Updated 8 November 2026

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The short answer

A puddle of clear water under the front of the car after a drive with the air con on is normal. That is condensation from the evaporator, and it does not mean the air con is leaking. Water in the footwell, usually on the passenger side, is not normal. The cause is then often a blocked, kinked or loose condensation drain. Have it fixed soon, because moisture in the car causes a musty smell and misted windows, and it can damage electrical parts.

Air con service at Autobedrijf Willemsbrug: from € 120 (R134a) or from € 180 (R1234yf), ready in 45 to 60 minutes. You can wait for it, on Saturdays too. You can also drop in if we have room: call +31 10 479 00 00 to check. For repairs, we tell you the price in advance. Our team speaks English. More about our air con service

Why does your car air con produce water?

The air con produces water because it does not only cool the air in the car, it also dries it. Behind the dashboard sits the evaporator, a kind of small radiator that the cold refrigerant flows through. According to the ANWB (the Dutch motoring organisation), the evaporator gets cold and damp as soon as you switch the air con on. Moisture from the air settles on the cold fins, like drops on a cold glass.

That water collects in a tray under the evaporator. A small hose, the condensation drain (also called the AC drain), carries it through the bulkhead between the engine bay and the cabin to the outside. There it drips onto the ground under the car. The warmer and more humid the weather, the more water comes out of the drain.

For the same reason the air con helps against misted windows, in winter too. You can read more about that in our article misted windows? Switch the air con on (in Dutch).

Water under the car: when is it normal?

Water under the car is normal if it is clear, has no smell and lies under the front of the car after a drive with the air con on. The Škoda Fabia owner’s manual puts it plainly: condensation from the evaporator may drip down and form a puddle under the vehicle. That is normal and not a sign of a leak. The puddle usually lies roughly under the dashboard, often slightly towards the passenger side. After you park, it keeps dripping for a while.

Is the fluid coloured, does it feel oily or sticky, or does it smell sweet? Then it is not condensation. Use the table to identify the fluid. More colours are explained on our page fluid under the car: what each colour means.

What you see What it probably is What to do
Clear water, no smell, only after driving with the air con on Condensation from the air con Nothing. This is normal
Coloured fluid (pink, green, blue or yellow), sweet smell Coolant Check the level with a cold engine and have the car checked
Brown or black, oily patch Engine oil Check the oil level and have the car checked
Thin blue fluid that smells of alcohol Screenwash Have the hoses and the reservoir checked
No water under the car in warm weather with the air con on Possibly a blocked condensation drain Check the footwell for damp

A first clue. If in doubt, put a piece of cardboard under the car and look at the colour and the position.

Pay special attention to the last row. Have you driven on a warm, humid day with the air con on and is there not a drop under the car afterwards? Then the water may be going the wrong way: inside.

Water in the footwell: usually the condensation drain

Water inside the car from the air con is usually caused by a condensation drain that no longer drains the water properly. The tray under the evaporator then fills up and the water finds another way out, usually into the passenger footwell. HELLA, a large supplier of car parts, describes this in technical notes for the Lexus IS and the Mini F56, among others.

  • Blocked. Dust, pollen, leaves and bacterial growth from the evaporator tray clog the drain. For the Lexus IS, HELLA names a blocked condensation drain as the cause of water in the interior.
  • Deformed or kinked. On the Mini F56, a deformed rubber seal can stop the condensation from draining properly. If there are kinks or traces of water, the drain has to be replaced.
  • Loose. After work on the dashboard, the heater or the engine bay, a drain hose can come loose or be routed wrongly.
  • Blocked from the outside. On some cars the drain outlet is under the car. Mud, a damaged undertray or a wrongly fitted cover can close it off.

Signs that fit this problem: a wet or soggy floor mat on the passenger side, a sloshing or gurgling sound behind the dashboard when cornering or braking, drops or splashes from the air vents, a musty smell and windows that mist up quickly.

Why you should not ignore a wet footwell

Moisture in the car does more than give you a wet mat. So have it checked within a few days. These are the consequences we take most seriously:

  • Damage to electrical parts. In many cars there are connectors and control units under the carpet and behind the dashboard. For the Volvo S80, HELLA describes a short circuit in the electric auxiliary heater caused by a blocked condensation drain.
  • Mould and a musty smell. Wet insulation under the carpet dries slowly. That gives a musty smell that lingers. Read more on our page about air con cleaning for a musty smell.
  • Misted windows. A car with a lot of moisture inside mists up quickly and is slow to clear.
  • Rust. Water that stands on the floor pan for a long time can cause rust in the long run.

Is the water really coming from the air con?

Not all water in the car comes from the air con. An easy test: does the mat only get wet after driving with the air con on, or after rain or a car wash? In the second case the cause is usually somewhere else.

When does it get wet? Possible cause What to look for
After driving with the air con on, also in dry weather Blocked or loose condensation drain Wet mainly on the passenger side
After rain or the car wash Blocked drain in the tray under the windscreen, a leaking windscreen or door seal, or a sunroof drain Leaves under the wipers, water along the door pillar or the headlining
Even with the air con off, with a sweet smell or a greasy film on the windscreen Leaking heater matrix (coolant) A coolant level that keeps dropping

A first clue. Coolant inside the car needs checking quickly.

Is there a sweet smell in the car and a greasy film on the inside of the windscreen? Then the heater matrix may be leaking. The air con does not cause that. Have the cooling system checked. Is the heater also less warm than it should be? Then read our page car heater blowing cold.

What can you do yourself?

You can find out where the water comes from and limit the damage yourself. Clearing the drain is best left to a technician.

  1. Look under the car. Drive for a quarter of an hour with the air con on and park on a dry spot. If there is a puddle of clear water under the front afterwards, the drain is working.
  2. Feel under the mat. Lift the floor mat on the passenger side and press the carpet underneath with your hand. If it is wet or soggy, water has already got in.
  3. Switch the air con off until it has been repaired. Without cooling, much less condensation forms. Do use the air con briefly if the windows mist up and you cannot see well. Safety comes first.
  4. Remove leaves under the windscreen. Are there leaves in the tray under the wipers? Take them out. That helps with water that gets in after rain.
  5. Let the car dry out. Take wet mats out and leave the windows slightly open in dry weather.
Do not poke blindly into the drain with a piece of wire or a screwdriver. The evaporator and the tray sit directly behind the opening and are easily damaged. A hole in the evaporator means a refrigerant leak and an expensive repair. HELLA also points out that on some cars the drain is hard to reach.

How we fix water in the car from the air con

We first find out where the water comes from and then clear or replace the drain. You receive a quote in advance and we only carry out repairs once you have agreed.

  1. Finding the cause. We check whether the water comes from the air con or from a seal, the tray under the windscreen or the heater. If in doubt, we run the air con for a while and watch where the water goes. If the water comes in through a seal or the bodywork, we tell you where to go for that repair.
  2. Clearing or replacing the drain. We locate the outlet of the condensation drain, clear it carefully and check the hose for kinks, cracks and a proper connection. If it is deformed, we replace it.
  3. Cleaning the evaporator if there is a musty smell. A blocked drain often goes together with bacterial growth on the evaporator. In that case we recommend cleaning the system.
  4. Checking the cabin filter. A clogged or wet cabin filter holds on to moisture and smells. According to the ANWB, a new filter costs € 40 to € 125 at a garage. We tell you your price in advance on your registration number. Read more about cabin filter replacement.
  5. Drying and checking. We advise you on how to let the carpet dry properly and check whether any connectors or control units have got wet.

Would you like the cooling checked at the same time, or is an air con service due? On our page about car air conditioning in Rotterdam you can read what it includes. Not sure whether the air con is still cooling properly? Then read car air con not cold or blowing warm air. Is a part of the air con itself faulty, for example the evaporator? Read more about air con repair. Is the air con also cooling less well, while the system has no leak? Then read about an air con regas.

Frequently asked questions

Is it normal for water to drip under my car when the air con is on?

Yes. That is condensation from the evaporator. It is clear, has no smell and lies under the front of the car. It does not mean the air con is losing refrigerant.

Why is there no more water dripping under my car?

In cold or dry weather the air con produces little condensation. Then it is normal for nothing to be under the car. If there is nothing on a warm, humid day after a drive with the air con on, the condensation drain may be blocked. Check the passenger footwell in that case.

Can I keep driving with water in the footwell?

Yes. For a short time that is usually not a problem. Keep the air con off as much as possible to produce less condensation. Do have it fixed soon, because moisture under the carpet can damage connectors and control units and causes mould.

Is the air con leaking refrigerant if water comes out?

No. The water comes from the air in the car and not from the air con system. Refrigerant is a gas, so it does not form a puddle. You notice a refrigerant leak because the air con cools less well.

Why is water spitting out of the air vents?

Usually the tray under the evaporator is full because the condensation drain is blocked. The fan then blows drops along with the air. In very humid weather you may also briefly see a puff of mist from the vents. That is cold, damp air and is harmless. If real water comes out, have the drain checked.

What does it cost to fix a blocked condensation drain?

That depends on how easy the drain is to reach and whether parts need replacing. We do not quote an amount without knowing the car. Call with your registration number and you receive a quote in advance. We only carry out repairs once you have agreed.

Does an air con service help against water in the car?

No. An air con service refills the refrigerant, but does not clear the condensation drain. With water in the footwell the drain has to be checked and cleared. If the air con also smells musty, cleaning the evaporator helps.

Wet mat or water from the air con?

Call +31 10 479 00 00 with your registration number or drop in for a quick check. You receive a quote in advance and we only carry out repairs once you have agreed.

You will find us at Boterdiep 11 in Rotterdam-IJsselmonde, close to Stadion Feijenoord (De Kuip). We work by appointment. For a quick question or check you can walk in without an appointment.

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