Valves on a Residential Water System and Where Each Belongs
Why this matters
The fastest way to turn a faucet swap into a flooded kitchen is to close an angle stop that has not moved since the house was built. The packing lets go, the stem snaps, or the washer stays on the seat and the stop never closes. A plumber who reads the valves on the way in, knows which ones can be trusted, and has a backup before turning the first handle does not have that afternoon. This card walks the supply from the street to the fixture, names each valve by type, says why it belongs where it is, and says how each one fails.
The supply from the street in
STREET CURB STOP utility owned,
main ---------[X]------- needs a curb key
|
| service line
foundation wall |
----------------+---------------------------
|
[ball] meter-side valve
[METER] (some utilities add a
[chk] dual check here)
[BALL] MAIN, full-port ball
|
[PRV] pressure reducing valve
|
+---------+--------------+
| |
[ball] heater cold to cold
| inlet, required branches
[WH] |
| [stop] angle stop,
hot branches under each fixture
| quarter-turn or
[stop] hot angle stop multi-turn
The drawing is the common basement-meter layout. In warm climates the meter sits in a box at the curb and the main shutoff is on an outside wall or in the garage; the order of the parts is the same.
Each valve, its job, its type
Curb stop. Belongs to the water utility in most places and is operated with a long curb key down a curb box. It is the only valve that isolates the whole service line, including the part inside the foundation. A plumber should not operate it without the utility's permission where the utility claims it, and should never force a seized one; a broken curb stop is a street dig at the utility's call.
Meter valves. Many installations have a valve on the street side of the meter, the house side, or both. The utility may own them. A dual check valve at the meter, installed by many utilities for backflow protection, turns the house into a closed system, which is why an expansion tank shows up later; see Expansion Tank Sizing for Closed-Loop Domestic Water Heaters.
Main shutoff. The one valve the homeowner should be able to find and close in a minute. IPC Section 606 and UPC Section 606, as adopted, require in substance a full-open valve on the building supply near where it enters; check the adopted edition's wording. The right valve is a full-port ball valve: a quarter turn closes it, the handle position shows its state from across the room, and a full port means the valve's bore matches the pipe so it adds almost no restriction. A standard-port ball valve has a bore about one size smaller, which on a 3/4 in main is a measurable pressure drop at full flow.
Gate valve (recognize it, then plan around it). A round handle, multi-turn, rising or non-rising stem, found as the main on most houses older than the 1990s. Inside, a wedge slides down across the flow. It was the full-port option of its day. It fails in two ways: the packing leaks at the stem when it is finally turned, and on old valves the wedge separates from the stem, so the handle spins and the gate either stays up (will not close) or drops and stays down (will not open). Either way the house is now dependent on the curb stop.
Globe valve (recognize it). Also round-handled and multi-turn, with a body that bulges at the seat. It closes by pressing a washer onto a seat, so it throttles well and shuts tight when new, but the flow path makes two turns through the body and it restricts more than a gate or ball valve. It has a flow direction arrow; installed backwards, line pressure sits on the stem packing when it is closed, and a washer that works loose can be pushed down onto the seat and shut off the flow. Found as old mains, old heater valves and the old straight stops. Not the right valve for a main or a heater inlet on new work.
PRV. Holds house pressure under the code limit, with static pressure at fixtures not over 80 psi as the shelf's number; see The Pressure and Temperature Numbers on Every Residential Call. It is not a shutoff and should never be used as one. Replacing it needs a valve on the street side, which is the main.
Heater cold inlet valve. The IPC and UPC both require, in substance, a shutoff on the cold supply to the water heater, so the heater can be drained and replaced without shutting off the house. A full-port ball valve here too. A valve on the HOT outlet is allowed but never substitutes for the cold one, and any valve placed between the heater and its T&P valve is prohibited; the relief path is owned by The T&P Discharge Pipe and the Rules Other Trades Break.
Fixture stops. Angle or straight stops under each sink and toilet, and integral stops on many shower valves. The codes require, in substance, a shutoff for each fixture or group of fixtures in a dwelling; the adopted edition sets which fixtures. Two families:
- Multi-turn compression stops. A washer on a stem, like a small globe valve. Cheap and serviceable, and the one most likely to fail when turned after years: the washer hardens and sticks to the seat, the packing weeps, and the stem can snap in a brass body softened by dezincification.
- Quarter-turn stops. A small ball inside. Closes in a quarter turn, position visible, much less likely to seize. The standard replacement and the right choice on new work.
Washer valves, hose bibs, ice maker supplies. A washer box with two quarter-turn valves is preferred to two multi-turn valves the customer never closes. Piercing saddle valves for ice makers clog, leak and are not permitted under many local rules; a tee and a proper quarter-turn stop is the fix when one is found.
The rule for any valve that has not moved in years
Treat every untested valve as a valve that might not close and might not open again. Before turning it:
- Know the next valve upstream, and confirm it works or can be reached. For a fixture stop, that is the main. For the main, that is the curb stop and whoever is allowed to turn it. If you do not have that, you do not have a backup, and the job waits until you do.
- Have the replacement in hand. A replacement stop or valve of the right connection type, a cutter, and the means to make the joint. Closing an old stop "just to see" without the parts on the truck is how a 30 minute job becomes an overnight water outage.
- Turn it gently. On a multi-turn valve, back the handle a little OPEN first to break the stem free, then close slowly. If it binds hard, stop. Forcing it is what snaps stems and drops gates.
- Watch the packing nut. A weep at the stem when a valve moves is normal on old valves; snugging the packing nut an eighth of a turn usually stops it. A spray means the packing is gone and the valve gets replaced from the upstream side.
- Confirm the close at the fixture. Open the faucet downstream. A valve with a handle in the closed position that still passes water is not closed.
Worked example: a kitchen faucet in a 1970s ranch
The ticket was a kitchen faucet swap. The plumber read the valves on the way in.
- Kitchen stops: multi-turn compression angle stops, chrome over brass, with a green crust at the packing. Not turned in decades by the look of them.
- Main: a 3/4 in gate valve with a round handle in the basement, just past the meter.
- Curb stop: in a curb box at the property line. The local utility allows licensed plumbers to operate it with notice.
- Heater: a globe valve on the cold inlet.
Plan before turning anything. The plumber told the customer the stops would likely need replacing and the main might not hold, and that the curb stop was the backup. Two quarter-turn angle stops in the right size for the existing pipe and a curb key were on the truck.
What happened. The hot stop closed and held. The cold stop turned a full five turns and the faucet still ran, so the washer had parted from the stem. The plumber went to the main. The gate valve turned eight turns and then spun freely, and the faucet still ran at a reduced flow: the gate had separated and stopped partway down. The curb stop was closed with the key, the faucet ran dry within a minute as the line drained back, and the work could start.
What was done. Both angle stops were replaced with quarter-turn stops, the faucet was installed, and before the curb stop was reopened the plumber quoted the main. With the customer's yes, the 3/4 in gate valve was replaced with a full-port ball valve while the water was already off, which cost the job about 45 minutes and saved a second outage later. The globe valve on the heater was noted on the ticket as a future replacement. The water came back on slowly at the curb stop to avoid a hammer surge, both new stops and the new main were checked dry at full pressure, and every faucet in the house was run to purge air.
Why the sequence worked. The backup existed before the first handle moved, the parts were on the truck, and the main was fixed while the cost of fixing it was lowest. The main replacement steps are owned by How to Replace a Main Shutoff with a Ball Valve.
What changes the answer
Private well. On a well system, the "curb stop" is the pressure tank's isolation valve and the pump's circuit breaker, both on the homeowner's side; the backup plan uses those.
Condo or townhouse. The main for one unit may be in another unit, in a mechanical closet, or not exist. Find out from the association before closing anything, because the upstream valve may cut water to several homes.
Old galvanized or brass. A valve threaded into old galvanized pipe may not come out without the nipple behind it breaking. Plan the transition before you start; see How to Transition from Galvanized to Copper or PEX.
Commercial or larger services. Mains above 2 in are often butterfly or resilient-seat gate valves, and the backflow assembly on the service has its own test cocks and isolation valves owned by a certified tester. Different card.
References
- IPC 2021 Section 606, Installation of the Building Water Distribution System, as adopted
- UPC 2021 Section 606, Valves, as adopted
- See related: Your Home's Shutoffs: Water, Gas and Electric
- See related: How to Replace a Main Shutoff with a Ball Valve
- See related: Expansion Tank Sizing for Closed-Loop Domestic Water Heaters