How to drive through flood water

Driving in heavy rain can be challenging, but flooded roads are even more treacherous. Be prepared with our guide to driving in the wet

James Mills
Sep 24, 2021

A recent report from the British Meteorological Office confirmed what many of us already believe, that the UK is already experiencing disruptive climate change.

In the last 30 years, says the report, we’ve become almost one degree Centigrade warmer, and 6% wetter. According to the lead author of the UK State of the Climate Report, that means we’re going to see ‘more and more extreme weather such as heatwaves and floods’.

2020 was our fifth wettest year on record, and plenty of drivers will have experienced the difficulties of driving in monsoon-like rainfall conditions. Excessive rainfall naturally leads to a far greater likelihood of rivers and waterways flooding, and that suggests more drivers will be facing the threat of flooded roads in the years ahead.

Flooded roads are already a common problem in the UK, simply because many are insufficiently drained and can’t cope with cloudbursts, while others are situated close to waterways that burst their banks. Many drivers will be familiar with local spots that become flooded and impassable during extreme rainfall.

Most cars, and even many SUVs, are not designed to cope with significant amounts of water on the road. Every year drivers suffer extensive and often irreversible engine damage because they’ve been bold or foolish when confronted with a flooded road, and taken a chance that they’ll get through it unscathed. Tragically, other drivers have died when entering floodwaters that have swept away their vehicles. You can read our handy guide to the best cars for driving through floods if you're in need of a more suitable car.

If rain is lashing down, it's wise to ask yourself whether you really need to travel at all before even leaving the house. Driving in heavy rain, flooding or not, can be pretty stressful and treacherous in itself, so if it's not urgent, you might be better off waiting until the rain has eased off. If it is essential though, we've put together this handy guide to driving in flooding that might just help to keep you afloat.

These 10 tips will not only help to keep you and your passengers safe, they will also help you to avoid what can often be irreparable damage to your car. The best advice when confronted by significant floodwater on the road is not to enter it, but to seek an alternative route. If that’s not possible, extreme caution is required, so read on to learn more about how to drive through flooding if it just can’t be avoided...

10 tips for driving in flooding

1. Don't forget your headlights

This is surprisingly easy to forget, especially if you're driving during the day. However, while you might not think to put your headlights on, it's important to make yourself visible to other drivers, especially during particularly heavy rainfall where visibility could be greatly reduced. Your headlights will of course give you a better view of what obstacles lie ahead.

The Highway Code says drivers must switch on their vehicle’s headlights when visibility is reduced, including in heavy rain. While it might not help you to see necesarily, it'll make you more visible to other road users. Even if that simply stops another vehicle zooming through a flood, causing a big wave to wash over your bonnet and destroying your engine, you'll be grateful for being seen.

2. Adjust your speed

You may be driving in a new off-roader or sports car fitted with a brand-new set of tyres, but you should always allow for conditions, which means slowing down in heavy rain. If that means dropping below the speed limit of the road, so be it. Fail to do this and you could experience aquaplaning, at which point you will be entirely out of control and could potentially lead to a crash.

Those who have ever experienced aquaplaning – where the tyres skate over the surface of standing water, creating an effect similar to driving on ice – will know that this can happen at even low speeds and leaves you with very little ability to steer or brake.

Reducing your vehicle’s speed reduces the likelihood of aquaplaning but also affords you more time to react to hazards in poor-visibility situations and the increased stopping distances that come with wet and flooded roads.

The same goes for following another car, you should allow double the distance between you and the car in front when driving in very wet weather to accommodate for the worse visibility and greater stopping distances.

3. Avoid severely flooded roads

It makes sense to avoid flooded stretches of road by taking detours where practical. Doing this means there’s no chance of you getting stuck or damaging your car; in certain conditions getting stuck in a flood could be potentially dangerous as you or your vehicle could be carried away in fast-moving water.

This also avoids the risk of damaging the underside of your car on unseen obstacles or, worse still, causing irreparable damage to the engine that could lead to your insurer declaring the car a write-off.

Remember, too, that if you were to write off your car this is likely to mean losing any no claims bonus you have on your insurance and/or still owing a substantial amount on your car finance, even if the insurance company pays out the market value of your car. Read our guide to Gap insurance to understand the risks.

One small caveat here is to make sure the alternative route is not similarly impassable, sometimes it is best to turn back along roads you know rather than delving deeper into leeser-known territory.

4. Gauge how deep the water is

If you have no option but to pass through flood water, don’t enter it without knowing how deep it is. This calls for some improvisation on your part. Find a stick or use an umbrella to assess the depth of the water.

Be mindful that the water is likely to be full of silt and you won’t be able to see where you’re driving, so use the stick to feel ahead, then take a measurement at the deepest part of the water. You can also use the stick to establish whether there are any high kerbs or hidden underwater obstacles ahead.

Next, compare the watermark on your stick, umbrella or even your leg to the ground clearance of your vehicle. If the water is as high as the lowest part of the car’s bodywork or higher, think twice about attempting to pass through it. The air intake for the engine could be flooded, which in turn could cause the engine to be destroyed.

5. Beware of strong currents

The current of floodwater running across a road can be surprisingly strong even if the water is only a couple of inches deep. That’s because there is so little friction slowing the water, due to the road’s smooth surface.

Be extremely wary of entering fast-flowing water, as anything above 15cm (nearly six inches) could sweep you off your feet or drag your car into danger and it could be impossible to either get back onto your fleet or regain control of the car.

6. Can anyone guide you?

If you have a passenger, or other drivers are about, it's a good idea to ask someone to guide you when crossing flood water. That’s because you won’t be able to see how high the water is and how it’s gathering around your car.

Having someone guide you means you don’t have to try to lean out of the window or leave your door ajar to see how high the water is in relation to your car, which could take your attention away from other hazards.

7. Go slow

Speed is your worst enemy in deep water. The likes of the AA, RAC and Land Rover advise entering flood water at speeds of only 1 or 2mph. You may need to slip the clutch slightly to do this, or dab the brakes in a car with an automatic gearbox to avoid going too fast.

This might sound extreme, but it will prevent a wave of water going over the bonnet and potentially causing irreparable damage to the engine. It can help to rev the engine a little as you slip the clutch, to keep the car moving slowly but also stop water flowing up the exhaust’s tailpipe.

8. Look out for approaching vehicles

You might be extra careful as you drive through flood water but what about other drivers? If there is an over-enthusiastic driver zooming towards you from the other direction, you need to take action to avoid them causing damage to your car.

Beware of a wave from their car, as it could swamp your car, causing water to entirely submerge the bonnet and engine. If you can see another car is passing through flood water you're approaching, therefore, it's wise to wait until they're through before starting yourself, so you're not in the water as they pass, which means that even if they create a humongous wave, you're safe.

9. Dry your brakes

As soon as you have passed through deep water, apply the brakes lightly to dry them off and ensure that no small stones have become lodged between the brake discs and pads.

This should mean that the next time you need to brake sharply, you'll get a better response, as the brakes shouldn't have such a layer of water on them, reducing their effectiveness.

10. Protect your engine

If the engine cuts out when crossing water, don’t try to restart it. It is likely to have swallowed water, and further damage could be caused by trying to start the engine again. If the car's still moving, try to move it as far out of the way as you can and switch on the hazard warning lights, so it can be seen.

If you urgently need to get clear of the vehicle, grab your phone and coat and get out. Don’t worry about water entering the car; this could help stabilise it. Once clear of the water, call a breakdown provider.


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