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Home›Guides›Water leak sensors
Where to put them, how an alert reaches you, and valves that act on their own without being asked.
A sensor two feet from where water actually arrives is a sensor that never fires. Placement matters more than specification.
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A small sensor under a washing machine costs about as much as a takeaway. A washing machine that empties itself onto a kitchen floor overnight costs several thousand and takes months to put right.
There is no feature to weigh up and no ecosystem to commit to. The only real decisions are where they go and how the alert reaches you.
The step beyond is an automatic shut-off valve; a device on the incoming main that closes when a sensor triggers. Considerably more expensive, and the only arrangement that helps when nobody is home.
In detail
Sensors go where water would first appear, not where it would end up. Tap a room.
What to watch for appears underneath
General guidance on placement. Every house is arranged differently.
Worth knowing
This is where the cheap sensors and the useful ones part company.
The simplest devices beep where they sit. That works if somebody is home and awake, and is worth nothing at two in the morning or during a fortnight away. These are the ones sold in packs for very little, and they are better than nothing.
Most useful sensors speak a low-power protocol to a hub, which then sends a notification to a handset. Battery life runs to years because the radio is only doing a few bytes a day, and the alert reaches you wherever you are.
Some sensors join the Wi-Fi directly, which removes the hub but shortens battery life considerably. Under a sink or in a loft, a battery that wants changing twice a year becomes a chore that gets forgotten.
A point that matters more than any of the above. A sensor tells you. It does not stop anything. If a pipe fails while the house is empty, an alert on a handset in another country changes nothing at all. That is the entire argument for a shut-off valve, and it is why the two are usually discussed together.
Practical
Considerably more involved, and the only thing in this category that acts rather than reports.
A shut-off valve fits on the incoming water main and closes on command. Paired with sensors, a leak anywhere in the house stops the supply within seconds rather than hours.
All of them need a manual override, and everyone in the house should know where it is. A valve that closes while nobody understands why is its own kind of emergency.
Plumbing is plumbing. Anything that involves cutting into a water main is work for a qualified plumber, and in some places is regulated. This page describes what these devices do; it is not a fitting guide and does not attempt to be one.
Before you buy
Tap a question to read the answer.
A sensor on a low-power protocol commonly runs two to five years on a coin cell or a pair of AAs, because it spends nearly all its time asleep and sends almost nothing.
A sensor that joins Wi-Fi directly does considerably less well — often under a year. That matters more than it sounds when the device lives behind a washing machine.
It should not. These detect liquid water bridging two contacts, not humidity in the air, so steam alone will not trigger one. A sensor sitting in a puddle from a shower splash, however, will do exactly what it is designed to do.
Placement matters: beside the pan and under the basin rather than in the middle of the floor where the shower drips.
Depends where the intelligence sits. A hub that decides locally can still sound an alarm and, if paired with a valve, still close it. A system that routes every decision through a manufacturer's servers may do neither.
This is one of the few categories where that question has real consequences, and it is worth asking before buying.
Arguably more so. A leak in a flat damages the property below as well as your own, and the liability question that follows is unpleasant for everyone.
Sensors need no permission and leave no mark. A shut-off valve on communal pipework is a different matter and would want the freeholder's agreement.
Keep reading
A leak sensor protects property. Smoke and CO alarms protect people, and the distinction matters.
Read the alarm guideHow we checked this
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