Driving through floodwater and heavy rain can feel quite perilous at the best of times, often catching out newer drivers or those who don't have any experience with driving in adverse conditions.
Rain and cars aren't always a match made in heaven, but with our quick and easy guide, you'll feel better equipped to navigate these tricky driving situations.
How to drive in heavy rain
Driving in the rain doesn't need to be stressful. As long as you follow our advice and remember that stopping distances increase in wet weather, you should be fine.
- Turn your headlights on – the Highway Code says you must use them when visibility is seriously reduced (less than 100m)
- Use fog lights if necessary, but switch them off when visibility improves
- Leave twice as much space between you and the car in front – it takes longer to stop in the wet
- If your steering feels light due to aquaplaning, ease off the accelerator and slow down gradually
- If you break down don't prop the bonnet open while you wait. Rain-soaked electrics can make it harder to start the engine
- If the rain is extremely heavy, consider waiting until it dies down (if you can) or avoid driving altogether
How to drive through floodwater
If you hear there's flooding on the way, try to move your car to higher ground to stop it from getting damaged. Water plays havoc with vehicle electrics and could cause several issues (like your airbag suddenly deploying for no reason).
If you encounter floodwater, our advice is to avoid driving through it. If you feel you have no other option, then be sure to follow these tips:
- If possible, try to avoid standing water.
- Don't drive into flood water that’s moving or more than 10cm (4 inches) deep.
- Let approaching cars pass first
- Drive slowly and steadily (around 3-4 mph) so you don’t make a bow wave
- Use higher revs than usual
- Keep the car moving and avoid stalling
- Test your brakes as soon as you can afterwards
- Fast-moving water is very powerful – take care or your car could be swept away
Some roads may have a depth gauge which shows you the level of flooding – this can be useful for seeing if you'll comfortably make it through or not. If you do get stuck in flood water, it's usually best to wait in the car and call for help rather than try to get out.
We provide 24/7 roadside assistance.
Why slow down in flood conditions?
Driving fast through water is dangerous, inconsiderate and can end up being very expensive.
Your tyres can lose contact with wet roads, causing you to lose steering control. This is called aquaplaning. If you feel it happening, hold the steering lightly and lift off to slow down gently until your tyres grip again.
At anything above a slow crawl, you’ll cause water to splash onto pavements – soaking pedestrians or cyclists. You could be fined and get points on your licence for this.
It only takes an egg cup full of water to be sucked into your engine to cause significant damage. For many cars, the engine’s air intake is low down at the front, making it quite susceptible to water damage.
What depth of water can a car drive through?
Generally, it's not advised to drive through water deeper than 10cm, unless you have a 4x4 that sits slightly higher than the average vehicle.
What should you do after driving through floodwater?
First off, check your brakes – they can become clogged after driving through water. You should test the brakes by applying them while moving to dry them off.
If you've driven through significant floodwater, then you should arrange for immediate garage attention to check over all the important parts of your vehicle.
If you need to leave the vehicle:
- Look out for slip and trip hazards like kerbs under the water
- Be aware that maintenance hole covers can get lifted and moved
- Water levels can change quickly
- Assume that flood water is contaminated
Types of floodwaters and their effects:
- Urban flood water can carry dangerous bacteria from drains and sewers that could cause disease.
- Rural flood water is more likely to be contaminated by agricultural chemicals and animal waste.
Fords
Just because the road goes into the river on one side and comes out on the other, that doesn’t mean a ford is safe to cross. The depth and speed of the water changes with the weather.
More on safely fording a river.
What might happen if you drive into floodwaters?
Depending on the level of the floodwater, your car may get swept away, causing irreversible damage to the integral parts of the vehicle and posing a threat to the lives of all occupants.
Sustaining flood damage to your car isn’t the only thing you need to worry about. Some other things that could happen include:
- Damage to your car's electrical systems
- Reduced or no braking
- Aquaplaning, which can cause you to lose control of your vehicle and crash
- You can hit objects hidden under the water (e.g. maintenance hole covers that have come loose in the flood)
- At lower water levels, you might splash pedestrians, which could get you fined
How do I know if water got into my engine?
There are a few key symptoms to look out for if you think water has gotten into your engine. These are:
- A fast, cranking sound or whirring when you turn the key in the ignition
- An abnormally strong smell of petrol, especially near the exhaust pipe
- Your car won't start at all, or starts briefly and stops again
What’s the AA’s stance on driving through floodwater?
We encourage people to avoid driving through floodwater wherever possible. If an AA member finds themselves with floodwater damage to their vehicle, we could offer assistance by providing a quote for recovery to a repairer of their choice (once their vehicle is clear of the flood). Alternatively, we would advise our member to contact their insurer for further guidance.
Floodwater facts
- Most drowning deaths happen within only 3 metres of a safe point
- Two thirds of those who die in flood-related accidents are good swimmers
- A third (32%) of flood-related deaths are in vehicles
- Cold water reduces your muscle strength – 20 minutes in water at 12 ºC lowers muscle temperature from 37 ºC to 27 ºC, reducing strength by 30%
- Just 15 cm of fast-flowing water can knock you off your feet and be enough for you not to be able to regain your footing
- It's a challenge to stand in waist-deep water flowing at only 1 m/s. By 1.8 m/s (4 mph) it becomes impossible to stand
- If the speed of the flood water doubles, the force it exerts on you or your car goes up four times
- 60 cm of standing water will float your car
- Just 30 cm of flowing water could be enough to move your car
- A mere egg cup full of water could be enough to wreck an engine
- Floodwater can be contaminated and carry diseases
- Culverts (tunnels carrying water under a road) are dangerous when flooded – the siphoning effect can drag in pets, children and even fully grown adults
Checklist for driving in heavy rain and adverse conditions
If you know you need to drive in heavy rain or bad weather conditions and you can't avoid it, make sure to carry out the following checks on your vehicle before you get going:
- Check the equipment of your car (e.g. windscreen wipers, headlights, fog lights, rear lights/brake lights)
- Check the tread of your tyres if you haven't already (worn tyres are less likely to grip on wet surfaces)
- Visibility is key, so ventilate your car if the windows are fogged up
- Test your brakes before setting off
- Drive slowly to avoid losing control on wet surfaces – your reaction time may not have changed, but the reaction time of your car increases in wet weather (e.g. braking takes longer, which is why it's important to maintain a larger distance between yourself and the car in front)
Can heavy rain damage a car engine?
Most cars are designed to withstand regular amounts of rain, but if flooding happens then it can be a big problem for your car's engine. If flooding occurs and there's standing water, for example, this can get into your engine and cause critical damage. If possible, always avoid driving in heavy rain or floods.
Broken down?
Member or not, we can help. Call us 24/7 on 03330 046 046.
Last updated: 03 July 2024