The five shut-off valves you should locate this weekend.

Maintenance tasks happen at scheduled intervals on calm days. The five shut-off valves come into play almost exclusively in the kind of moment you cannot schedule — a burst supply line, a failed water heater, a toilet that will not stop running, a leak under a sink that the family in the upstairs apartment cannot identify the source of. The cost of locating the valves before any of those moments happens is a Saturday afternoon. The cost of locating them in real time, while water is moving from inside the wall to outside it, is roughly five thousand dollars for every thirty seconds it takes you to find the right one. (Our editorial estimate, based on actuarial work and the cost of two ceiling-and-floor replacements we have done in the houses of friends; your mileage may vary.)

This is a piece of the broader project of household plumbing literacy — the small unsexy weekend rituals that prevent emergencies, like the kind of attention we paid in our bathroom fan piece. The five valves are the load-bearing item in that project. Locate them once. Mark them with a permanent marker on a paper tag, looped to the valve with a zip tie. Exercise them annually. The five-minute version of this work, repeated each February, pays back over decades.

The single most important valve in the house. Closes the entire water supply, everywhere. The valve every first-time homeowner thinks they know how to find and then, in the actual moment, does not. Locate this one first.

Where it lives.

In most US houses, the main shut-off is in the basement, on the supply pipe that enters through the foundation wall, within about two feet of the wall and within about three feet of the water meter (if the meter is inside). In houses without a basement (slab construction), it is often in a utility closet, in a garage wall, or in an exterior valve box buried at the property line. In some warm-climate houses with no basement, there is no household shut-off at all and the only shut-off is at the meter, which usually requires a meter key (a special wrench you should buy for ten dollars at the hardware store and keep on a shelf).

What it looks like.

One of two shapes: a gate valve (a round wheel handle, on a vertical or horizontal stem, that turns multiple times — twelve to twenty-five rotations — to close completely) or a ball valve (a single straight lever handle, that turns exactly 90 degrees from open to closed). Houses built since about 1995 almost always have ball valves; older houses often still have gate valves. Both work; ball valves are faster (one-quarter turn vs. two dozen turns) and less likely to stick over time.

How to close it.

For a gate valve, turn the wheel clockwise (as you face the handle from the operator’s side) until it stops; do not over-torque past the stop. For a ball valve, turn the lever until it is at 90 degrees to the pipe (perpendicular = closed; parallel = open). Old gate valves sometimes seize completely; if yours is stuck and the situation is not an emergency, spray penetrating oil (Liquid Wrench, PB Blaster), wait fifteen minutes, try again, and consider replacing the valve with a quarter-turn ball valve next time a plumber is in the house. An old gate valve that has not been turned in a decade is often the valve that will refuse to close when you need it to close.

A ball valve, almost always, on the cold-water inlet at the top of the water heater. The most common reason to use it: the heater itself is leaking, dripping, or about to fail, and you want to stop water from continuing to fill the tank while you wait for the plumber. The second most common reason: a homeowner replacing the heater’s anode rod, drain valve, or T&P relief valve — small once-a-decade repairs that should not require shutting off the whole house.

Find it now. Stand in front of the heater. Look at the two pipes coming out of the top of the tank — one cold (often blue paint, or otherwise unmarked) and one hot (often red paint). The cold inlet has the shut-off valve, usually within about six inches of the tank top. If your heater does not have a shut-off on the cold inlet, that is itself worth flagging: modern code requires one, and adding one is a one-hour plumber visit. A water heater without a dedicated shut-off is the appliance most likely to teach you the painful version of why a dedicated shut-off matters.

One per toilet, on the small braided supply line that runs from the wall to the bottom of the tank. The single most-used shut-off in any first-time homeowner’s house, almost always for the same reason: the fill valve has failed and the toilet will not stop running. (The other common reasons: replacing the wax ring at the base, swapping the seat, replacing the whole toilet.)

Two shapes: the modern 1/4-turn ball valve (small chrome lever, 90-degree turn to close) and the older multi-turn stop (small oval or football-shaped chrome handle, three to five rotations clockwise to close). The multi-turn stops are reliable when new and infamous for seizing or for leaking through the stem packing after twenty years of disuse. If you have not touched yours in this decade, do not test it for the first time in a moment when the toilet is overflowing. Test it now. If it does not turn smoothly, a $14 SharkBite or Brasscraft 1/4-turn replacement is the right next plumber visit; the swap is twenty minutes and turns a multi-decade liability into a small piece of insurance.

Two valves under every sink in the house, one hot and one cold, on the small supply lines that feed the faucet. The most common reason to use them: replacing the faucet itself, replacing the P-trap, replacing the supply lines (the braided stainless ones eventually wear out — about every fifteen to twenty years), or stopping any of the small leaks that happen under any sink over time.

The same two shapes as the toilet shut-offs apply: modern 1/4-turn ball valves (the right shape) and older multi-turn stops (the failure-prone shape). The difference at the sink is that you have two of them, and the muscle memory of “left is hot, right is cold” matters when the kitchen is dim and the cabinet door is open and there is water on the floor. Mark them now: a small piece of red electrical tape on the hot, a small piece of blue on the cold. The mark you put on the valve in February will save you a minute in October.

When the old ones won’t turn.

Old multi-turn sink stops are the second most common stuck valves in any first-time house (after the multi-turn toilet stops). Penetrating oil, fifteen minutes, gentle pressure with a 6-inch crescent wrench is the first attempt. If it still won’t turn, do not force it past breaking — the stem can snap, which turns a small problem into a soldering-and-shutoff-at-the-main problem. The right move is to close the valve upstream (the main, if needed) and replace the stop with a 1/4-turn ball valve the next time a plumber is in the house.

In the basement or crawlspace, on the supply line that feeds the outdoor faucet, usually directly inboard of the wall the faucet exits. The valve used twice a year — closed in the fall to winterize the outdoor faucet, opened in the spring when you want the garden hose to work again. Also the valve you close any time you fix the outdoor faucet itself — for the rubber-washer repair walked through in our outdoor-faucets fix, this is the first step before any wrench touches the faucet body.

In some houses, especially those with frost-proof sillcocks installed since about 2002, there is no separate indoor shut-off for the outdoor faucet — the frost-proof design has the valve seat moved inboard of the wall, theoretically eliminating the need for a separate valve. We still recommend installing one. Frost-proof sillcocks fail in their own ways (worn seats, packing nuts, vacuum breakers), and the small inboard shut-off lets you isolate the faucet for any of those repairs without shutting down the whole house.

The whole inventory, on a five-valves-by-five-questions table, fits on a single page. Use it as the field guide for the Saturday-afternoon walk-through. Tag each valve, mark each one’s location on the table, exercise each one, and put the table inside a cabinet door in the kitchen for future reference.

The five-minute February ritual.

Once a year, in February (when nothing else is happening in the house, and the heating system is reminding you that household systems exist), walk the inventory and turn each valve through its full motion — closed, then open again. The five valves total about five minutes. The valves that move freely are doing their job; the valves that resist are the early warning that something needs penetrating oil or, occasionally, a plumber. The valve that moves freely this February will move freely next October, when you need it.

The order an emergency happens.

When a leak announces itself at an inconvenient hour, the order is: smallest containable valve first, main last. A leak under the kitchen sink — close the two sink shut-offs under the cabinet (cold first if the leak is on the cold supply, both if you cannot tell). A leak from the toilet — close the toilet shut-off behind the tank. A leak from the water heater — close the water-heater inlet. Only when the small valve does not close, or when the leak is in a wall and you cannot reach a smaller valve, do you close the main. Closing the main is a successful response to an emergency; closing the main first when a small valve would have worked is a successful response that left the rest of the family without water for the next two hours.

Five valves. One Saturday afternoon. The cheapest insurance any first-time homeowner can buy, and the one that returns in full the night something fails.