The water heater leaked. Stopping the damage in the first two days.
A 50-gallon tank does not stop at 50 gallons. The cold line keeps refilling it until somebody closes the valve, so a leak that starts at midnight is still running at six.
Updated October 2026
Stop the water first
Close the cold water valve above the heater, then turn off the gas control or the breaker. If the valve will not turn, close the main where the water line comes into the house. The steps, and which way each valve turns, are here.
If water still comes out after that, the tank is emptying what it already holds. Put a garden hose on the drain valve at the bottom and run it to a floor drain or out a door.
Before you walk into it
Look at where the water has gone before you step in it. Ready.gov's flood guidance is short on this point. Do not touch electrical equipment if it is wet or if you are standing in water, and turn off the electricity if it is safe to do so.
In a basement that means power strips and extension cords on the floor, the outlet behind the washer, the dehumidifier, and anything plugged in near the heater. If the electrical panel is in the wet area, or you would have to stand in water to reach it, leave it alone and call an electrician or your electric company.
The heater counts too. Bradford White's manual says not to use a water heater if any external part of it has been under water. If the water rose around the bottom of the tank, leave the heater off until a plumber has looked at it.
Get the water up
A wet vacuum is the fastest tool most houses have. Plug it in somewhere dry. A mop and towels do the same job more slowly. If the basement has a floor drain, push the water toward it with a broom.
Pick things up off the floor as you go. Cardboard boxes, rugs and anything made of fabric soak water up from the bottom and hold it against the floor.
Take photographs before you move anything or throw it out. The reason is under what the insurer expects.
The two-day clock
The EPA's guide to mold gives the number that matters. Dry water-damaged areas and items within 24 to 48 hours to prevent mold growth.
Run fans across the wet floor. Put a dehumidifier in the room and empty it as it fills. Keep both going after the floor looks dry.
Water does not stay where you can see it. It runs under the baseboard into the bottom of the wall, and it soaks the pad under a carpet while the top only feels damp. The EPA names the back of drywall and paneling and the underside of carpet and pad among the places mold grows out of sight. Pull the carpet back at a corner and look. Press on the bottom few inches of the wall.
Hard surfaces can be dried and cleaned. Absorbent ones are the problem. The EPA says materials such as ceiling tiles and carpet may have to be thrown away if they become moldy.
Do not paint or caulk over a stain while the surface is damp or moldy. Clean it and dry it first.
When it is past a mop and a fan
Some leaks are more than a household can dry in two days:
- a finished basement with carpet, drywall and insulation
- water that came through a ceiling from a heater upstairs
- a leak that ran for hours while nobody was home
A water damage company brings pumps, air movers, large dehumidifiers and meters that read moisture inside a wall. This site does not recommend one. Your insurance agent can tell you how your company handles it.
On mold, the EPA's rule of thumb is that a patch smaller than about 10 square feet, roughly three feet by three, is something most people can clean up themselves. Past that size, or after a lot of water damage, the EPA sends you to its guidance for larger jobs. That is where most people hire it out.
If the heater sits above another apartment or unit, the damage is in two homes. That case is covered here.
What the insurer expects
The standard homeowners form, called HO-3, lists what the owner has to do after a loss. Three of the duties apply on the first day.
Give prompt notice to the company or your agent. Protect the property from further damage, which the form says includes reasonable and necessary repairs and an accurate record of what you spend on them. And prepare an inventory of damaged personal property.
So call your agent the same day. Keep the receipts for the fan rental, the wet vacuum and the plumber's visit. Photograph everything before it goes to the curb, and write down what it was.
The form generally covers the damage a sudden leak causes. It does not pay for the water heater. The wording is that the coverage does not include loss to the appliance the water escaped from. A leak that had been seeping for a long time before anyone noticed may be treated differently.
This describes the standard form, not your policy. Ask your agent how yours reads.
Then the heater
A tank that leaked from the body cannot be repaired. Rheem and Bradford White both say it has to be replaced.
In Massachusetts only a licensed plumber can replace a water heater, and the job needs a permit. In an emergency the plumber can do the work before the permit is issued, as long as the town inspector is notified and inspects by the next working day. The permit is still required.
So it does not happen twice
A pan under the heater, a leak alarm on the floor beside it, and an automatic shutoff on the cold line each cut the damage the next leak can do. How to keep a tank from leaking, and how to catch it early.