Updated 03 February 2014

Why a flood is such a killer

It doesn’t take a lot of water to cause a lot of trouble. Even 15cm of fast-flowing water can knock you off your feet; 60cm of water can float a car.


The danger from floods isn’t just the direct risk of drowning or injury from objects such as trees and vehicles flung with the floodwater.

Floods can destroy sewerage systems, causing raw sewage spills and drinking water contamination.

Buildings, storage facilities, transportation arteries and service lines can be damaged, releasing toxic materials such as paint, oil and petrol into rivers and the ocean, killing aquatic life and posing a human health risk.

People often lose their homes and livelihoods to floods, and become victims of psychological trauma, illness and crime – as well as financial devastation.

Floods can cause serious erosion to coasts, leading to sea water flooding and rendering them more vulnerable to future floods and erosion.

How to prepare for a flood

When travelling to a new area, read up on the potential risks of natural disasters for a particular place or season. Be aware of flood hazards no matter where you are, but especially in a low-lying area, near a water body or downstream from a dam.

Keep in mind that flooding can happen to even small streams, dry streambeds and low-lying ground that appear harmless in dry weather. Be aware of streams, drainage channels, canyons and other areas known to flood suddenly. Flash floods can occur in these areas without obvious warnings such as heavy rain.

Listen to news broadcasts at regular intervals if you are in flood season or if there is any flood risk. It is an excellent idea to keep a portable battery-powered radio with you.

Water-purifying tablets are also important to have with you: drinking water is often contaminated after a flood and needs to be treated.

Plan and practise a flood evacuation route with your family. Ask an out-of-town relative or friend to be the family contact in case your family becomes separated during a flood or other disaster. Everyone in your family must know how to get hold of this contact person.

If there is any possibility of a flash flood, move immediately to higher ground.

If a flood is imminent

Once a flood warning has been given, keep the radio on to hear emergency updates.

If authorities advise you to evacuate, depending on the amount of time available:

Fill portable containers with fresh water.

Turn off utilities (electricity, water, gas) at the main switches or valves. Disconnect electrical appliances (but don’t touch electrical equipment if you're wet or standing in water).

Move valuable items to an upper floor. Bring in outdoor furniture.

Flood water dangers

Don’t walk through moving water higher than about 15cm – this is enough to make you fall. If you have to walk through water, walk where it’s not moving. Use a long stick to check the firmness of the ground in front of you.

Avoid driving into flooded areas. If floodwaters rise around your car, abandon it and move to higher ground. The temptation may be to keep driving, but the vehicle can be quickly disabled and swept away:

- Six inches (about 15cm) of water will reach the bottom of most passenger cars causing loss of control and possible stalling.
- A foot (about 30cm) of water will float many vehicles. Two feet (about 60cm) of rushing water can carry away most vehicles, including 4-wheel drives.

If you are advised not to evacuate your home, or you are otherwise unable to leave, climb to the highest safe place and wait for rescuers to find you. Don’t try to swim outside in floodwaters. Time permitting, store fresh water in containers, and turn off gas and electricity.

After a flood

Avoid floodwaters: water may be contaminated, for example with petrol or sewage. Water may also be electrically charged from damaged power lines. Steer clear of power lines that have fallen down or seem damaged.

Be careful of areas where floodwaters have recently receded. Roads may have weakened and could collapse under the weight of a car.
Return home only when authorities say it's safe. Stay out of buildings still surrounded by flood waters. Be cautious when entering a building; there may be hidden damage. Watch out for slippery floors and debris.

Get damaged septic tanks and similar systems serviced without delay. Damaged sewage systems are serious health hazards. Clean and disinfect surfaces and objects that were touched by the floodwater. Mud deposited by a flood can contain sewage and toxins.

Don’t turn on your power until an electrician has given you the go-ahead.

Boil or disinfect tap water before use until the authorities announce that it's safe to use again. Plain, recently purchased liquid household bleach can be used if you have no other means of disinfection: add 2 drops of bleach for each litre of water, stir well and leave it to stand for 30 minutes before use.

- Olivia Rose-Innes, EnviroHealth Editor. @ORoseInn

Flood Safety Checklist (2009). Red Cross.
Dangerous water levels for walking and driving from the Federal Emergency Management Agency (FEMA), official website.
Turn around don't drown. NOAA National Weather Service, USA


Read Health24’s Comments Policy

Comment on this story
Comments have been closed for this article.

Live healthier

Looking younger »

Can maple leaves help you look younger?

New research has found that maple leaf extract can help you look years younger.

Killer foods »

Wild mushrooms a 'silent killer'

Health practitioners are warning people to stay away from wild mushrooms.