Is It Safe to Walk or Drive Through Floodwater?

No. The answer from every fire and rescue service, council and government body that has published on this is the same: never drive through floodwater, and never walk through it either. The water is usually deeper and faster than it looks, and it can hide hazards you cannot see. A car can float in just 30cm of moving water, and a foot of water moving at only 6 miles per hour is enough to take it¹.

If you meet a flooded road, turn around and find another route. That is the whole of the advice, and it holds whether you are in a car, on foot or on a bicycle. The risks are not theoretical: driving through water incorrectly can cause serious damage to your car and could put your life at risk³.

This page explains why the water is more dangerous than it appears, what to do if you have no alternative, and what to check afterwards. It also covers the questions people ask most often, from fords on country roads to the waves thrown up by larger vehicles.

Never drive through floodwater: find another route

The instruction is repeated across official guidance in every part of the UK. Never drive through floodwater, because it can be deeper or faster flowing than it looks⁶. Always find an alternative route². If you encounter unexpected and sudden flooding while driving, do not proceed: turn around and find another route⁷.

The same applies on foot. It is not safe to drive, walk or swim through floodwater⁸. Do not walk, drive or swim through flood water⁹. Even flood wardens, who are trained volunteers, are told not to drive or walk through flood water¹⁰. If the people who know the local area best will not enter it, that tells you something.

Why is the advice so absolute? Because the consequences of getting it wrong are severe. Driving through water incorrectly could cause serious damage to your car and could put your life at risk¹¹. Beneath the surface there may be hidden hazards: open drains, debris, kerbs that have been washed away, or a road surface that has collapsed¹². You cannot see any of this from the driver's seat.

There is also a practical point about travel. Official advice during a flood is to travel only if your journey is essential, to drive to the conditions and not to drive through floodwater⁵. If you are at home and a flood warning is in force, you should only evacuate yourself if it is safe to do so, and you should only travel if you really have to¹³. Staying put is often the safest choice.

Just 30cm of water can move a car

The figure that surprises people most is how little water it takes. A car can float in just 60cm of standing water or 30cm of moving water⁴. As little as 30cm of water can float a car⁵. The government's own national flood risk assessment puts it plainly: a depth of just 30cm of flood water can be enough to move a car during a heavy rainfall event¹⁴.

Moving water is the more dangerous of the two. A foot of moving water, moving at just 6 miles per hour, is enough to float a car¹. The Met Office gives the same warning: although the water may seem shallow, just 12 inches (30cm) of moving water can float your car, potentially taking it to deeper water from which you may need rescuing².

Once a car floats, the driver is no longer in control. The vehicle can be carried sideways into deeper water, and the occupants may then need rescuing by the fire and rescue service. That is a risk to the rescuers as well as to you.

Why floodwater is deeper and more dangerous than it looks

Floodwater is not like a puddle. It can be much deeper than it appears and can hide dangers such as open drains, debris and damaged road surfaces¹². When faced with a flooded road, you cannot always tell how deep the water is¹⁵. That uncertainty is the reason the advice is to avoid it altogether rather than to judge each crossing on its merits.

The guidance from councils and fire services is consistent. Only drive through water if you know that it is not too deep¹⁶. Never drive through water if you are not sure how deep it is, as this could result in your car becoming stranded¹¹. Do not attempt to cross if the water seems too deep: look for an alternative route¹⁷. Do not drive through flood water, because there could be hidden hazards and it may be deeper than it looks¹⁸.

There is a further danger that catches people out: the road itself may no longer be there. Floodwater can wash away the surface, undermine the edges and leave holes that are invisible from above. The guidance to avoid walking, swimming or driving through floodwater exists because there may be hidden dangers¹⁶.

If you are on foot, the same rules apply. Do not enter flood water unless it is absolutely necessary. If you must enter flood water, move slowly and carefully, avoiding fast-moving water¹². But the better answer is not to enter it at all: find another route, or wait.

If there is no alternative: drive slowly in a low gear and keep moving

The official position is that you should not drive through floodwater at all. But guidance does exist for the rare case where a driver has no alternative, and it is worth knowing what it says, because it explains why a casual crossing goes wrong.

If you have to drive through floods, drive slowly using first gear and keep the engine revving at a high rate, moving forward continuously to avoid stalling¹⁹. In an automatic, engage and hold in a low gear¹⁹. Drive slowly and steadily so you do not make a bow wave, and test your brakes as soon as you can afterwards²⁰. If you decide to proceed, drive slowly in first gear but keep the engine speed high by slipping the clutch¹⁷.

Why the low gear and high revs? Because water in the exhaust could otherwise damage the catalytic convertor²¹. Going slowly and using a low gear also means you do not make waves or get water in your engine²². The aim is a steady, continuous movement that keeps the exhaust gases pushing water out and avoids the stop-start that stalls an engine.

If you are driving a larger vehicle, do not go through flood water at speed, because this creates a bow wave that can cause flooding to adjacent properties. A bow wave is the wave pushed ahead of a moving vehicle; in a narrow street it can send water over doorsteps and into homes that would otherwise have stayed dry.

After driving through water, check your brakes

Always check your brakes after driving through water³. Test them as soon as you can afterwards, once you are back on dry road and it is safe to do so²⁰. Brakes that have been submerged can behave differently for a while, and you need to know how they are responding before you rely on them at speed.

If your vehicle has been damaged by floodwater, get it checked by a professional mechanic. Do not attempt to drive your car without having it checked²³. Water can get into places you cannot see, and a car that seems fine immediately after a crossing may develop problems later.

Look out for standing water and adjust your driving before and after encountering any¹⁸. That means slowing down before you reach it, and being cautious for a while after you have passed through it, because your brakes and steering may not feel normal straight away.

Moving your car to higher ground, and other questions

Should I move my car before the water arrives? Yes, if it is safe to do so. During a flood, move vehicles to higher ground²². But do not drive through flood water to do it: only move your vehicle to higher ground if it is safe to do so²⁴. If the road is already under water, leave the car and protect yourself instead.

What about fords on country roads? Do not drive through flooded roads or fords. Water is often deeper than it looks and may be moving fast, and vehicles may be swept away or stranded²⁵. A ford that is passable in dry weather can become dangerous within minutes of heavy rain.

What if I am on foot and the water is only shallow? The advice does not change with depth. It is not safe to drive, walk or swim through floodwater⁸. Do not walk, drive or swim through flood water⁹. Avoid walking, swimming or driving through floodwater²⁶. If you need to get somewhere, find another route.

What about fast-moving water across a road? Do not try driving through fast-moving water, such as at a flooded bridge approach, because your car could easily be swept away²⁷. Moving water is the most dangerous kind, and a bridge approach is exactly where it can be deepest and fastest.

Should I travel at all? Only if your journey is essential⁵. During a flood you should only travel if you really have to¹³. If you are at home, staying put is usually the safest option. If you need to leave, do it before the water arrives, not through it.

For what to do if water is coming into your home, see What to Do During a Flood at Home. For the warning stages and what they mean, see Flood Alerts, Flood Warnings and Severe Flood Warnings. If you are in Wales, Natural Resources Wales Warnings and Risk Maps sets out how warnings work there. For help during a flood, see Help During a Flood²⁴.