What to Do in a Flood: Before, During and After

Woodbury Center, Connecticut, around half past three in the morning on September 2, 2021. The remnants of Hurricane Ida had put three to seven inches of rain across the Hudson Valley and western Connecticut in a few evening hours, and the National Weather Service’s storm report for that night records a state trooper’s vehicle swept away by flood water.

A marked car. A trained driver. A road he had almost certainly driven before.

Which tells you what to do in a flood better than any list does, because it says where the danger actually sits. Not in the rain, and not in the depth. In a decision made in the dark about a road you cannot see the bottom of. So the sequence below follows the clock: the quiet afternoon, the hours when the alerts arrive, the night itself, and the weeks afterward when the money is decided.

Before the water: three lookups and one afternoon

Nothing in this section is urgent, which is exactly why it never gets done.

Start with the map. FEMA’s summary of what flood maps do is one sentence — flood maps show how likely it is for an area to flood — and its threshold is just as short: any place with a 1 percent chance or higher chance of experiencing a flood each year is considered to have a high risk. The Flood Map Service Center looks up an address free and returns a code, decoded further down with the thirty-day clock attached.

Then the house. Ready.gov’s before-a-flood list is four lines and every one of them is an afternoon’s work: move valuables to higher levels, declutter drains and gutters, install check valves, consider a sump pump with a battery.

That last one earns its own sentence, because a sump pump’s failure mode is not that it breaks. It is that the grid goes down and the pump stops at exactly the hour it was bought for. A battery backup for a sump pump^aff. is the dullest purchase on this site and one of the few that does its whole job while nobody is home. When the outage outlasts the water, the rest is in extended power outage.

The check valve is the line people skip and regret: a barrier across a doorway holds the street out and does nothing about the sewer coming back up through the floor drain. A plumber’s job.

And the paperwork, once — policy numbers, the deed, prescriptions, photographs of every room, in something you can carry upstairs in one hand. The criterion there is that it closes and stays closed while someone runs up a staircase, which an ordinary folder does not and a zippered expanding document case^aff. does. The list is in important documents in an emergency.

Watch, warning, emergency: three words, three different clocks

Ninety seconds of vocabulary that changes behavior more than any object here, and most households have the first two backwards.

The National Weather Service definitions are short enough to quote whole. A Flood Watch is issued when conditions are favorable for a specific hazardous weather event to occur. A Flood Warning is issued when the hazardous weather event is imminent or already happening — a Flash Flood Warning, when a flash flood is imminent or occurring. A Flood Advisory is issued when a specific weather event that is forecast to occur may become a nuisance.

Above all of them sits one more. A Flash Flood Emergency is issued for the exceedingly rare situations when extremely heavy rain is leading to a severe threat to human life. If you see that word, the discussion about whether to move is over.

The alert	What it means	What it changes at home
Advisory	May become a nuisance	Change the plan for the drive. Nothing else.
Watch	Conditions are favorable	Car to high ground. Basement emptied. Bag by the door.
Warning	Imminent or happening here	Go up. Nobody goes outside, nobody drives.
Emergency	Severe threat to life, now	Highest floor immediately, with a phone and a light.

Why the watch is the one to act on

A flash flood watch, says the Weather Service’s product list, indicates current or developing conditions favorable for flash flooding. That is the whole window, and it is short: flash flooding is defined as flooding that begins within 6 hours, and often within 3 hours, of the heavy rainfall. Three hours is not enough to move a car, find a barrier, clear a basement and decide where everyone sleeps. It is barely enough for one of them.

So the watch is when I would act, and the warning when I would stop moving. Not quite the official framing — officially a watch only means possible — but it produces the right behavior in a tired household on a Tuesday night, and the cost of acting early is an evening carrying boxes upstairs for nothing. The same asymmetry, with minutes in the place of hours, is what tornado safety turns on.

The alert also has to reach you, and flash floods are disproportionately nocturnal. A phone on silent in another room is not an alerting system, and neither is a cell tower whose generator has run dry — which is the case for an emergency weather radio.

While the watch is up, the physical job at the door is sealing the gap underneath it — not with sandbags nobody has, but with water-activated flood barrier bags^aff., which store flat in a closet and swell when they get wet. They buy a ground floor a few inches and an hour. They do not argue with a river.

What to do in a flood once the water is already moving

Everything above was optional. This part is not, and it is three sentences long.

Ready.gov’s during-a-flood guidance opens with the instruction that overrides everything else here: evacuate immediately, if told to do so, and never drive around barricades. That call belongs to local officials, and there is no version where you decide they were being cautious. Being able to obey it in ten minutes rather than an hour is a separate skill, and the loading order is worked out minute by minute in a wildfire evacuation.

Second: do not walk, swim or drive through flood waters. Turn around, don’t drown.

Third: get to the highest level if trapped in a building, and only get on the roof if necessary — once there, signal for help.

The rest of this page exists so those three sentences are executable in ten minutes instead of forty, by a household that already knows which floor everyone is going to.

Turn Around, Don’t Drown: the arithmetic of a two-ton car

The campaign has a name because the failure has a pattern. The National Weather Service puts four sentences on one page: a mere 6 inches of fast-moving flood water can knock over an adult; it takes just 12 inches of rushing water to carry away most cars; 2 feet of rushing water can carry away SUVs and trucks; and over half of all flood-related drownings occur when a vehicle is driven into hazardous flood water.

Over half. Not in rivers, not in basements. In cars, driven in voluntarily.

People drive in because the numbers feel wrong. A foot of water reaches the middle of a hubcap; a car weighs two tons; the intuition says the car wins. But the car is not fighting the water. It is being weighed against it.

Water weighs about 62 pounds per cubic foot. A midsize sedan is roughly sixteen feet long and six feet wide, so once the water rises above the floor pan, each additional inch displaces something like forty cubic feet and takes several hundred pounds off the tires. By twelve inches most of the vehicle’s weight is in the water rather than on the road, the friction holding it in its lane has fallen with it, and a current at walking pace pushes on sixteen square feet of sheet metal with more force than that friction can answer.

The tool below draws it, to scale, an inch at a time.

Turn Around, Don't Drown — the arithmetic

At what depth does your car stop being a car?

Pick the vehicle, raise the water an inch at a time, then say whether it is standing or running. The drawing is to scale and the three forces underneath are the ones that decide the night: what the water has lifted, what is left on the tires, and what is pushing sideways.

Compact sedan 3,000 lb Midsize sedan 3,500 lb Crossover SUV 4,200 lb Full-size pickup 5,200 lb

Depth of water on the road 0 in

06 in12 in18 in24 in30 in

Is the water moving?

Standing 3 mph 6 mph

Pick a vehicle to start the drawing.

Two things it makes visible that prose does not. How late the curve turns — nothing for the first few inches, which is the part that feels safe, then everything at once. And that a truck is not immune, only delayed: ground clearance buys inches, not permission.

At night none of it is measurable anyway. You cannot see whether the road is still under the water, and often it is not: a culvert scours the roadbed out from below and leaves a surface that looks continuous and is a hole.

Inside the house: what to shut off, and what never to touch

The instruction from Ready.gov has no conditions on it: do not touch electrical equipment if it is wet or if you are standing in water. The CDC adds the move that belongs to the calm half-hour beforehand — unplug appliances to prevent electrical shock when power comes back on.

Together those make a rule about timing rather than courage. Cutting the main breaker is something you do early, from a dry floor, with dry hands, while the water is still outside. Once it is inside, or once the panel itself is wet, that option has expired: leave it alone and call the utility, who can kill it at the meter. Gas has the same shape — if you smell it, everyone goes outside first and the call is made from outside.

And nothing submerged goes back into service on household judgment. Outlets, breakers, the furnace, the water heater, the washer: wet equipment does not dry out into safe equipment.

Go up, not out

The instinct worth rehearsing is vertical. Not out to the car, not down to the basement for the boxes, not into the parking garage for a vehicle worth less than the person going to get it.

Below-grade space fills from the ramp or the stairwell, fast, against a current running the way you want to walk. A basement apartment with one door and window wells is the worst room in the building on the worst night of the year, and the time to notice that is a dry afternoon.

What goes up with you fits in one armload.

Documents go in something that closes. A roll-top waterproof dry bag^aff. takes the pouch, the phone and a charger, seals in one motion, and floats — which matters in a stairwell. The rest of what belongs by the door is in the go bag checklist, with the reasoning in the go bag guide.

Light is the other one, and the phone is the wrong tool for it, because the phone is how you get found. A waterproof rechargeable headlamp^aff. per person leaves both hands for a railing, a child, a bag. Lamps and batteries are inventoried post by post in the 72-hour emergency kit.

Then water, because the tap is the first thing a flood makes unusable and the last thing anyone plans for: a gallon per person per day, kept upstairs rather than in the basement where it always ends up. The staircase is the constraint that decides the format, which rules out the five-gallon drum nobody can lift and argues for stackable two-gallon containers^aff. — emergency water storage covers doing that in an apartment with no spare room.

After: the water leaves and the rules arrive

The morning after looks safe and is not. Ready.gov’s line on coming back has no flexibility in it: return home only when authorities say it is safe. Roads that look intact may have nothing under them, lines may be down and live, and the building you are walking into has been sitting in contaminated water for a day.

On the cleanup the guidance is specific about clothing — wear heavy work gloves, protective clothing and boots — and worth taking literally, because the hazard is not the water but everything it carried in. Knee-high rubber boots and heavy work gloves^aff. are two things to own before the day you need them, since every hardware store within forty miles will be out of both.

Photograph first. Every room, every wall, every ruined object, before a single thing goes into a bag. That is the evidence a claim runs on, and it cannot be reconstructed later.

Then the triage, which the CDC makes simple: throw away items that cannot be disinfected, like wall coverings, cloth, rugs and drywall. Porous goes, hard and sealed stays — and drywall comes out higher than the visible line, because paper wicks. The CDC’s line on the tap is just as short: listen for local officials on how to safely use water to drink, cook or clean, because a flood can contaminate a system without changing how the water looks or tastes.

Then the part that takes months rather than days. A building still wet inside its walls in week three is a mold problem rather than a flood problem, and the tool is a dehumidifier with a continuous drain^aff. running with the windows shut. Open windows in humid summer air add water to a room.

The thirty days nobody mentions until it is too late

This is where households lose the most money for the least reason.

Your homeowners or renters policy excludes flood. Not limits — excludes. FEMA’s own page says most homeowners insurance does not cover flood damage, and Ready.gov repeats it in the same breath as the advice to buy one: homeowner’s insurance policies do not cover flooding. Rising surface water in your living room is not a covered peril on a standard contract. A burst pipe, or rain through a hole the storm made in the roof, is a different peril with different rules.

Coverage comes from the NFIP, and it takes about thirty days. FEMA’s wording is to plan ahead, as there is typically a 30-day waiting period for an NFIP policy to go into effect. It is sold by ordinary insurance agents, and it is available to anyone living in one of the 22,600 participating NFIP communities. Renters is the part almost nobody knows: you can insure contents without owning the building.

Your zone letter is not a verdict on your risk. It is a statement about a study, drawn on the rainfall record that existed at the time, and water from a blocked storm drain does not consult the legend first.

The decoder below reads your letter back to you, including the part it does not say, and dates the thirty days from today.

The flood map, decoded

What does your flood zone letter actually say?

Type your address into the FEMA Flood Map Service Center and it returns a code. Click the one it gave you below and this reads it back in plain English — including the part the letter does not say, which is where most households get hurt.

AE High risk A High risk AO or AH High risk V or VE High risk, coastal X shaded Moderate X unshaded Minimal Not looked yet Two minutes

Do you already hold a flood policy?

Yes, I hold one No I am not sure

Pick the code the map gave you — or the last tile, if you have never looked.

What to do with all of it is one document and one phone call. The document is your declarations page: whether you hold any flood coverage at all, whether building and contents are both covered, and what the deductible is. If you cannot find those three lines, that is the phone call, and it takes five minutes.

What does not help, including the thing everyone pictures

The sandbag. It is the image every broadcast uses and it is close to useless for a household: a wall that holds needs hundreds of them, hours of labor, sand you do not have and a pallet nobody will deliver on the night of a warning. Municipalities use them because municipalities have loaders.

Then the barrier bought without the check valve: the half you can buy online is not the important half.

Then the sealed “flood kit” in a bucket — the same whistle and foil blanket sold to a household in Tampa and one in Tulsa, answering none of the lookups at the top of this page. What a household lacks is the count, the location and the floor they live on, which is what the emergency kit page is for.

And the last one, which sounds prudent: waiting to see how bad it gets before moving the car. Ten minutes at the watch. A car at the warning.

A dry afternoon in March

I would do it in one afternoon, in a month with no weather in it.

Look up the address, write the letter on a sticky note, and call the agent whose name is on the policy to ask the three declarations-page questions. That is the expensive half, and it is entirely phone work.

Then the physical half: the battery on the sump pump, the check valve quoted, the barrier bags in the hall closet with the door’s measurement on the packet in marker, the radio programmed to the county code, one shelf upstairs cleared for what must not get wet.

None of that is a bunker and none of it is a hobby. It buys the only thing worth having at two in the morning when the phone screams: nothing left to decide.

The same reasoning applied to the other hazards your county has is in natural disaster preparedness, and if your flood arrives attached to a named storm every September, hurricane preparedness starts a week earlier. When it stops being one bad night and becomes a season, that is long-term emergency preparedness.