SMART HOME BUTLER · BATHROOM
Water damage scales with time, not volume
The same loose hose is a job for a cloth if you catch it in five seconds, and a claim on your neighbour's ceiling if you find it four hours later.
The leak is not the problem — nobody noticing is
A washing machine drain hose works loose, a cistern seal perishes, a water heater fitting corrodes. None of these is rare. What they have in common is that they make no sound, produce no smell, and almost always happen with nobody in the room.
If you happen to be home and happen to walk past, it is a job for a cloth. If you are at work and get back four hours later, the water is over the bathroom threshold, the hallway floor is ruined, and there is a good chance it has reached the ceiling below.
The difference between those two outcomes is not how much water leaked. It is how long it ran unnoticed — and time is exactly what a sensor is good at.
What happens in those five seconds
- 0 sec
Water reaches the sensor
A leak sensor is two metal contacts that conduct when wet. There is nothing to judge and nothing to calculate — the state changes the instant it touches water.
- 1 sec
The system has the signal
Zigbee and Matter messages are effectively instant. The system now knows there is water on the bathroom floor.
- 3 sec
The valve closes
With a powered valve fitted, this is the single most valuable action in the whole setup. Cut off the source and the damage stops here.
- 5 sec
Your phone rings
The notification names the sensor and where it sits. Even from the other side of town you know what happened and whether to send someone round.
- 2 min
If you are home
You walk over and look. Nine times out of ten the washing machine hose has worked loose. Reconnect, dry off, clear the alert, done.
- Ongoing
If you are not home
The valve stays shut and the system re-alerts at intervals until somebody deals with it. It does not give up because you did not reply.
Where to put them
Leak sensors are small and cheap, and placing them well matters far more than owning lots of them. The rule is simple: put them where water must arrive first, which means the lowest point.
| Location | Most common cause | Priority |
|---|---|---|
| Under the washing machine | Drain hose works loose, inlet fitting perishes | Highest |
| Under the water heater | Corroded fittings, dripping pressure relief valve | Highest |
| Behind the cistern | Perished base seal, leaking fill valve | High |
| Inside the vanity unit | Loose trap connection, split flexible hose | High |
| Under the kitchen sink | Filter fittings, dishwasher drain | Medium |
| Inside the bathroom threshold | A last line of defence, catching water on its way out | Medium |
Four things it takes care of
Property
A soaked wooden floor means replacing the whole run, and a downstairs ceiling claim is worse. This setup exists to prevent that one-off large loss.
Neighbours
With a leak that reaches the flat below, the hard part is rarely the repair bill — it is the conversation. Stopping it early means there is no conversation.
Peace of mind
While you are away, something is watching the plumbing. It is the kind of thing you never notice until the day you are very glad of it.
Early warning
Many leaks start as a few drops. A sensor catches that stage, before it becomes a disaster, and gives you the chance to fix it cheaply.
What you need to have
| What it does | Category in the system | Essential? |
|---|---|---|
| Detect water on the floor | binary_sensor | Yes |
| Receive the alarm | notify (phone app) | Yes |
| Shut the water off | switch or valve | Strongly advised |
| Sound an alarm locally | siren or switch | Nice to have |
| Turn on a light | light | Nice to have |
How the whole thing works
Use the ready-made blueprint
The hub ships with 22 tested automation blueprints — think of one as a fill-in-the-blanks form. This uses binary_sensor_trigger_things, which exists for "something went from fine to not fine".
| Field | What it means | Suggested |
|---|---|---|
| Which sensors | All leak sensors — you can select several at once | — |
| On water detected | Close valve, notify, light up | All three |
| On clearing | Usually nothing; wait for a human | Leave empty |
| Active hours | This one cannot be time-limited | Always |
| Notifications | Required, at the highest priority | On |
One optional addition
| If you want | Blueprint | What it does |
|---|---|---|
| Keep reminding until dealt with | entity_state_trigger_notify | While a sensor stays wet, repeats the notification every fifteen minutes until somebody attends to it — so a message dismissed while you were busy does not end the matter |
Just say the word
The WOOWTECH hub ships with HA-MCP, so an AI can connect straight into your system and do the work: find the sensors, build the rules, then simulate a leak itself to confirm the valve really closes and the message really lands, and only report back afterwards.
Prompts you can copy straight out
Every block below can be copied whole, using the button on the right. Pick the one closest to what you want. There is no need to use them all.
I have a leak sensor under the washing machine and another under the water heater. If either one touches water, push an alert to my phone straight away, naming which sensor it is and where it sits. This rule should run around the clock, with no time window on it.
My leak sensors sit under the washing machine, under the water heater, behind the toilet cistern and inside the vanity cupboard. If any one of them touches water, close the powered water valve, push an alert to my phone, and turn on the bathroom light plus the siren if there is one. The alert must name which sensor and where it is, at the highest priority so do-not-disturb cannot suppress it. No time window and no extra condition on this rule: 3am counts exactly the same as 3pm. Also repeat the alert every 15 minutes while a sensor stays wet, and warn me if one runs low on battery or drops offline for a day. Once it is built, test it yourself, confirm it really works, then tell me which devices you used.
I have no powered water valve and the plumbing here cannot easily be altered, so build this with sensors alone for now. There are two of them, one under the washing machine and one under the water heater. If either touches water, alert me with sound rather than a quiet message, because I am usually out during the day. Turn the bathroom light on at the same time, so anyone at home sees it. If I fit a valve later, it should slot into this same rule without rebuilding anything.
Please adjust the leak rule. Make the repeat reminder every 10 minutes instead of 15, a quarter of an hour feels too long to me. I have also put another sensor under the kitchen sink. Fold it into the same rule rather than making a new one. And send the alert to my wife's phone as well, since I am not the only one here who can deal with it.
This leak rule has never once been put to a real test, so today I want a full rehearsal without spilling a drop of water. Make the system believe the sensor under the washing machine has gone wet. I will be standing right there watching all three things: the valve, the alert on my phone, the bathroom light. Report each one as it happens, and the moment one of the three fails to move, stop there and say so rather than carrying on. When it is over, turn the valve back open and set the sensor to dry.
Common questions
Flat on the floor, or raised?
Will shower splashes cause false alarms?
How often do batteries need changing?
If it shuts the mains, the whole house loses water
Is it worth it with no powered valve?
What if a sensor fails and I never find out?
The setup you hope never fires
It may not go off once all year. But the one time it does, it usually saves more than the entire smart home cost to install.
You will appreciate it most on the day you leave for a holiday.