A washing machine, dishwasher, or fridge is leaking.
Close the shut-off valve for that appliance, then unplug it. The valve is on the wall behind a washing machine, under the sink for a dishwasher, and usually behind or beneath the fridge for an ice maker line. You do not need the main valve unless you cannot reach the local one.
Where each valve is
Washing machine: a pair of valves on the wall behind it, hot and red, cold and blue, or a single lever that closes both. Close both.
Dishwasher: under the kitchen sink, on the hot supply line running to the dishwasher. There is often a second valve for the faucet, so follow the pipe.
Refrigerator ice maker: a small saddle valve or quarter-turn valve on the cold line, usually behind the fridge, under the sink, or in the basement directly below.
If none of them will close, shut off the main for the house. If that will not turn either, there are three other ways.
Why supply hoses are the usual culprit
The braided steel hoses feeding a washing machine are under house pressure every minute of every day, whether the machine is running or not. When one lets go, it does not drip. It delivers the full supply until someone closes a valve, which is why a washing machine hose failure while nobody is home is one of the more expensive things that can happen to a house.
The same is true of any appliance connected to a supply line. The machine being switched off does not make the hose safe.
Work out which kind of leak it is
Clean supply water, from a hose or fitting before the machine: the easiest case. Dry it fast and the damage is usually limited.
Drain water, from a discharge hose or a blocked drain: this is gray water. It carries detergent, food, and bacteria. Do not run a fan over it before it is cleaned, and keep it off anything absorbent you plan to keep.
Water from inside a dishwasher door seal or a washer door: usually smaller, but it has often been happening for a while, and the damage under and behind the unit is worse than the puddle in front of it.
Look underneath and behind, not just at the floor
This is where appliance leaks quietly get expensive. Water runs under the machine, under the cabinet kickboard, and into the particleboard the cabinet is made of, which swells and does not recover.
- Pull the machine forward if you can do it safely, and look at the floor underneath.
- Check the cabinet floor next to it, and the kickboard at the bottom.
- On an upper floor, check the ceiling in the room below.
- Feel the flooring at the edges of the room, not just at the spill.
If it is under a floating floor, water spreads sideways across the underlay and has nowhere to escape. That does not dry on its own.
Then dry it, quickly
The clock is the same as for any other water event. The window before mold becomes likely is 24 to 48 hours from when material got wet, and the trap is that surfaces dry long before materials do.
Photograph everything before you clean up, including the failed hose or fitting itself. A hose that visibly burst is evidence that the failure was sudden, which is exactly the distinction most policies turn on.
Worth doing afterwards
- Replace both washing machine hoses, not just the one that failed. They are the same age.
- Close the washer valves when you go away for more than a few days.
- If a fridge line runs through a floor or a wall to reach the ice maker, know where its valve is before you need it.
The short version
Close the appliance’s own valve, not the main. Kill the circuit before reaching behind anything standing in water. Look under and behind the machine, not just at the puddle. Photograph the failed part before it goes in the trash.