A burst supply line does not wait for a plan. Water runs until someone closes the valve that feeds the house, and in most houses that valve is a single fitting that few people have ever touched. Dad knows where it is because he has lived with it for years. The question for you is whether anyone else can find it in the dark, turn it, and know it worked, without calling him first.
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Trace the line from the meter
Do not guess at the location. Start at the water meter, which is usually near the street or at the front of the property, and follow the cold supply line from there to where it enters the house. The main shutoff is normally on that line, often in a basement, crawl space, utility room, or a wall where the pipe comes through the foundation. Some older setups place the main valve outside in a curb box, which needs a separate key and sometimes a permit to open. Write down exactly which situation applies to this house.
While you are tracing, note every other shutoff you pass. The water heater, toilet supplies, sink supplies, the washer hookup, and the icemaker line may each have their own valve. Mark which fixture each one controls. A burst line at the washer should not require shutting the whole house if a local valve exists.
Test the valve gently
Older houses often have gate valves, which have a round handle that takes many turns to close. Those can seize from years of no movement. A quarter turn on a stiff gate valve can be enough to show whether it moves at all. If it does not move, or if it grinds or feels like it will snap, stop. Forcing a seized valve can break it, and then you have no shutoff and a leak at the same time. Call a plumber to service or replace the valve and ask them to confirm the valve fully closes.
Lever-style ball valves usually need only a quarter turn. Test those the same way, then return them to fully open. Confirm the water still runs at a faucet after you reopen, so you know the valve did not leave the house dry or partly closed.
Clear the path and label it
The valve has to be reachable with a flashlight and an empty hand. Remove boxes, bins, and anything stacked in front of it. Put a clear tag on the valve and on each local shutoff that says what it controls. Keep a wrench that fits the valve nut in a set place near the valve if the design calls for one. Do not store it in a drawer on another floor.
Name the owner
Write one card with four lines: the location of the main, the location of the nearest local shutoffs, the name and number of the plumber you will call, and the utility emergency line printed on the water bill. Put the card where Dad keeps his own important papers and give a copy to the person who answers the phone at night. Name who closes the valve, who calls the plumber, and who pays. Those three names should be written down, not assumed.
Dad can keep his routine and his tools. What you are building is a house where the water can be stopped without him, and that is a different job from asking him to change how he lives.
What to ask the plumber
When the plumber is in the house for any reason, ask them to look at the main valve and tell you its type, its condition, and whether it fully closes. Ask whether the house has a pressure regulator or backflow device that needs its own check. Ask how old the braided supply hoses are on the washer and icemaker, and whether any of them show bulging or cracking. Ask what they would replace first if the budget were limited, and ask for the reasoning in writing before any work starts.
For the wider order of operations, see Start Here. Tonight, walk to the place where the water line enters the house, find the main valve, turn it a quarter turn and back, write its location on a card, and tape the card to the inside of the kitchen cabinet closest to the phone.