If water is running and you cannot stop it, close the main shut-off valve, then call. Everything else is secondary. For a burst supply line that means the main; for a leaking water heater it means the cold valve on top of the unit; for a backed-up drain it means stop using water in the house entirely, because every fixture you run adds to what is coming back up. Knowing where your main shut-off is — before you need it — is the single most useful piece of plumbing knowledge a homeowner can have.
First: find your main shut-off now, not later
Most people look for it for the first time while standing in water. Go and find it today.
In Sonoma and Marin, it is usually one of:
- A valve where the supply enters the house, often in a garage, crawlspace or utility area
- The meter box near the street or property line, which will have a valve on the street side
- An exterior wall valve near a hose bibb on older properties
Turn it, or at least confirm it moves. A great many main shut-offs in older North Bay housing are corroded gate valves that will no longer close — which you very much want to discover on a dry Tuesday rather than during a burst.
Burst pipe or major leak
- Close the main shut-off. Clockwise.
- Open a low tap — an outside bibb or a ground-floor sink — to drain pressure and let the line empty away from the break.
- Switch off electricity to affected areas at the breaker if water is anywhere near outlets, fixtures or a panel. Do not stand in water to do it.
- Move what you can out of the path.
- Call.
Water heater leaking
Close the cold supply valve at the top of the heater — that isolates the unit without shutting the whole house. On a gas unit, turn the gas control to off. On an electric unit, switch off its breaker; never leave an element energised in a draining tank.
If the heater is in a closet, upstairs, or anywhere above finished flooring, say so when you call. A tank can go from weeping to releasing its full 40 or 50 gallons in one step, and location changes the priority.
Backed-up drain or sewage coming up
Stop using water immediately — every fixture drains into the same system, and running the washing machine while the main line is blocked pushes more sewage into the house.
Do not keep flushing to see if it clears. Do not pour chemical drain opener into a fully blocked line; it sits there, and it is still there when someone has to work on it.
If sewage has surfaced, keep people and pets away from it and ventilate.
Useful to note when you call: is it one fixture or several? Several fixtures backing up together, or the lowest fixture in the house overflowing when an upstairs one drains, points at the main line rather than a branch.
Suspected gas leak — different rules entirely
This one is not a plumbing call first.
Leave the building. Do not switch anything on or off, including lights. Do not use a phone inside. Then call 911 or your gas utility from outside.
Once the utility has made the site safe, the repair itself is licensed plumbing work. But evacuation comes first, every time.
What helps us when you call
- Where the water is coming from, as precisely as you can tell
- Whether you have been able to shut it off
- Whether it is one fixture or several
- Where the affected area is — ground floor, upstairs, above finished ceiling
- Whether the property is on septic, because a slow drain on septic often means the tank rather than the line
Related reading
- Leak detection and repair
- Clogged drain and sewer line clearing
- Water heater repair and replacement
- Gas line repair and leak detection
Frequently asked questions
My main shut-off will not turn. What now? Try the valve at the meter box on the street side. If neither closes, the water utility can shut the service. A seized main shut-off is worth replacing regardless — it is a small job and it is the valve you need on your worst day.
Should I use drain cleaner on a blocked main line? No. It will not clear a main line blockage, and it sits in the line as a hazard for whoever opens it.
Is a slow drain an emergency? Usually not on its own. Several fixtures slow at once, or sewage surfacing, is a different matter and should not wait.
What if the leak is outside, in the yard? Still close the main if it is on the supply side. Soft or unusually green patches in dry months often mean an irrigation or service line fault, which wastes a great deal of water quietly.