Guides · Safety

Flash floods: why six inches of water is the number that matters

6 min read · Updated September 2026

Flooding kills more Americans in a typical year than tornadoes, and more than half of those deaths happen inside vehicles. Nearly all of them come from a decision that felt reasonable at the time: the water looked shallow, the driver knew the road, it was only a short stretch.

The numbers are unforgiving. Six inches of moving water can knock an adult off their feet. Twelve inches can float a small car. Two feet will carry away most SUVs and pickups.

The short version

Six inches knocks you down, twelve floats a car, two feet carries a truck.
Turn around, do not drown, applies to roads you know well too.
During a flash flood warning, go up, never into a basement.

Why floodwater deceives

You cannot see what is under it. Moving water scours roadbeds from below, so a road that looks intact may be a hole. Water hides washed-out culverts, open manholes, downed lines, and debris.

You also cannot judge depth or speed by looking. Water moving at 10 mph exerts the same force on a car as wind at about 270 mph. Once tires lose contact, steering and brakes do nothing at all, and the vehicle goes wherever the current goes.

What to do at a flooded road

Turn around. The detour costs minutes; there is no version of this where crossing is the sensible risk.
Never drive around barricades. They are placed by people who know why the road is closed.
At night, treat any standing water as impassable. Depth is essentially unreadable in headlights.
If water rises around a stopped car, get out immediately and move to higher ground while the doors still open. Do not wait in the vehicle for it to recede.

Reading the alerts

Flash flood watch: heavy rain is expected and could cause rapid flooding. Move vehicles to higher ground and rethink travel.
Flash flood warning: flooding is happening or imminent. Get away from creeks, low crossings, and underpasses now.
Flash flood emergency: catastrophic, life-threatening flooding is occurring. Move to higher ground immediately and do not attempt to drive out of it.

If you live somewhere flood-prone

Know whether your street is in a mapped flood zone and how quickly the nearest creek rises. Local flood history tells you more than an average.
Keep the water heater, furnace, and electrical panel raised where that is possible.
Store documents, medications, and a change of clothes in a waterproof container you can grab in one motion.
Buy flood insurance before you need it: policies typically take thirty days to take effect, and home insurance does not cover flood.
Never shelter in a basement during a flash flood warning. Go up, not down.

Afterward

Floodwater carries sewage, fuel, and farm chemicals. Wash anything it touched, throw away soaked porous items such as mattresses and upholstered furniture, and dry the space within 48 hours to limit mold. Do not restore power to a flooded panel yourself.