Home Assistant water-leak detection with an automatic main shutoff

A slow drip under a sink is easy to miss until the cupboard floor goes soft. Give it a faster ending: sensor gets wet, Home Assistant closes the water main, and your phone tells you where to look. Start with a Zooz ZAC36 Titan, Home Assistant Connect ZWA-2, and Zigbee leak sensors on your existing radio. The first job is delightfully low-tech: meet your valve.

Research guide: hardware details and setup steps come from the makers, Home Assistant and the linked integration projects.

First, meet the valve you want to turn

Open the cupboard or access panel and find the valve that isolates your domestic water supply. You’re looking for a quarter-turn ball valve with a lever handle, rather than a wheel you wind through several turns. Read the size marking, look at the pipe support, and leave enough room for the actuator to grip the handle.

Zooz’s Titan fitting requirements specify 0.5–1.25-inch ball valves and these clearances:

Fit check	Space the Titan needs
Along the pipe	3 inches from the valve centre to each side
Handle above the pipe	At least 1.25 inches
Pipe away from the wall	At least 1 inch

Take a photo for your own shopping notes and compare the actual mounting area with the maker’s installation drawings. A valve squeezed against a wall needs attention before a motor joins the party. The Titan clamps over an existing valve; it isn’t a replacement plumbing valve.

Call a plumber if the valve is stiff or corroded, the pipe flexes, the mounting material is unsuitable, or you’re unsure which supply you’d be shutting off. Zooz specifically advises against mounting this actuator on CPVC and discusses support requirements for flexible PEX. Get a sound, accessible shutoff point first, then add the smart part.

Pick the kit, then choose your sensors

The main build is Titan + ZWA-2 + a Zigbee radio + the THIRDREALITY leak-sensor four-pack. Reuse your radio if you already have one. The SONOFF and Aqara sensors in the Parts lists are alternatives for particular spots, not extra purchases you must add to the base kit.

Part	Local connection	Pick it for
Zooz ZAC36 Titan	Z-Wave through Z-Wave JS	Turning a compatible main valve; includes a wired leak probe
Home Assistant Connect ZWA-2	USB Z-Wave adapter	Connecting the Titan to Home Assistant
SONOFF Dongle Plus MG24	USB Zigbee coordinator	Connecting the leak sensors when you need a radio
THIRDREALITY leak sensors, four-pack	Zigbee	Covering several spots with sensors that also have an audible alarm
SONOFF SNZB-05P cable bundle	Zigbee	Reaching an awkward gap with the selected detection-cable bundle
Aqara Water Leak Sensor	Zigbee	Reusing the sensor from your starter kit or adding a compact puck

Home Assistant lists the ZAC36 among its certified Zooz devices. The Z-Wave integration guide explicitly names ZWA-2 as an adapter option and explains the Z-Wave JS server and integration. Your Zigbee radio handles the sensors separately. Home Assistant joins their events to the Titan command, so a Zigbee sensor can close a Z-Wave actuator.

The THIRDREALITY sensor is the straightforward multi-spot pick: it uses replaceable AAA batteries and has a built-in alarm. The SONOFF manual describes floor placement and extension support; the linked Amazon configuration includes a detection cable. The original Aqara sensor is a useful reuse choice if you followed our starter-kit guide.

Already using Zigbee2MQTT? Keep that route. Its device pages list leak reporting for THIRDREALITY 3RWS18BZ, SONOFF SNZB-05P and Aqara SJCGQ11LM. The built-in ZHA integration is the simpler starting point for the existing starter-kit path. Give your coordinator to one Zigbee integration.

What about Aqara’s Valve Controller T1?

The T1’s maker-supported route uses an Aqara Zigbee hub, with a compatible Aqara bridge for Matter. Zigbee2MQTT also documents a direct VC-X01D route, while the candidate Amazon listing identifies VC-X01E. For that listing, plan around the documented Aqara-hub route. Keep the Titan/ZWA-2 build below if you want to follow this guide’s main setup.

Put the sensors where water will reach them

Think like the drip: where would it land, and where would it collect? Put sensing contacts on the surface you want to monitor, rather than on a shelf above it. Keep each sensor accessible for drying, battery changes and another test.

Spot	Useful placement	What to automate
Under a sink	A low, normally dry point beneath the supply connections or trap	Main shutoff request and phone alert
Washing machine	Floor near the hose connections, clear of feet and moving parts	Main shutoff request and phone alert
Water heater	A suitable dry point in the drain pan or adjacent floor, following the heater’s instructions	Main shutoff request and phone alert
Sump area	Normally dry floor beside the pit, away from equipment that moves	Phone alert for unexpected water

THIRDREALITY recommends spots near washers, water heaters, sinks and dishwashers. Use the SONOFF cable option when the sensor body won’t sit neatly where the first water would appear. Follow the cable and sensor instructions for positioning.

Keep the sump sensor out of the main-shutoff automation if it’s watching groundwater. Closing the domestic water valve won’t stop that water entering; the useful action is to get your attention. Add it to a separate alert-only automation instead.

Fit the Titan and pair the two radio paths

Choose a time when stopping the water supply is convenient. Follow the official Titan quick guide: close the valve before fitting the actuator, secure the fork and clamps, connect power and perform calibration. Keep the handle and mounting visible for the first opening and closing checks.

Connect ZWA-2 to your Home Assistant host and follow the discovered device’s Recommended installation workflow for Z-Wave JS. Use the correct radio region for your devices. To include the Titan, follow Settings → Connectivity → Z-Wave → Add device and the maker’s inclusion instructions. Keep a backup of your Z-Wave security keys as the integration guide recommends.

Then pair your chosen leak sensors through ZHA, or your existing Zigbee2MQTT setup. Use each maker’s pairing instructions, name the sensors clearly, and test them at their final positions. Sensor A, Sensor B and Sensor C are perfectly good temporary names while you work through the setup. Our coordinator guide covers MG24 placement and the other radio options.

Before making an automation, operate the Titan from its device page. Watch the handle close and verify that downstream water flow stops. Identify the exact action that closes it: Close valve for a valve entity, or the tested Turn on or Turn off action if it appears as a switch. Use that fixed command in the recipe; avoid Toggle. The Z-Wave JS device reference includes an invert-report setting, so establish the physical direction during setup.

Build “leak → close valve → phone alert”

Start with the sensor dry. Open Settings → Automations & scenes, then Create automation → Create new automation. Name it something obvious, such as Leak: shut off main water.

1. When → Add trigger: choose Moisture detected.
2. Add target: select the actual leak entities that should stop the domestic supply. Leave the sump alert-only sensor out.
3. Set Trigger when to Each, so any selected sensor can act. Leave For at least at zero for an immediate trigger.
4. Under Then do → Add action, add the Titan’s fixed closing command you verified above and select its control entity.
5. In that action’s Menu, select Continue on error, so an action error doesn’t stop the following phone alert.
6. Add your phone’s notify.mobile_app_… action and enter a Message: “Leak detected. Main shutoff requested. Check the water and valve.” The Companion notification guide covers the action and notification permissions.
7. Save the automation. Leave reopening as a deliberate manual action after you’ve found and dealt with the water.

Each matters here: you want the first wet sensor to act, rather than waiting for every target to get wet. The message also stays useful if the valve is unavailable or a command fails—it tells you to inspect the situation without claiming the supply has already stopped.

The damp-paper-towel test

Make the first leak a tiny one you control. Tell anyone relying on the water that you’re testing, keep the actuator visible and have a clear way to restore the supply.

• Check the phone first. Use the notification action to send a test message. Enable the Companion app’s notification permission and check that the phone receives it.
• Prove the sensor-to-alert path. Temporarily disable the closing action in the editor and press Save before testing. Touch a damp, non-dripping paper towel across the sensor’s sensing contacts. Watch Home Assistant change to wet and receive the phone message. Keep water away from power connections.
• Prove the shutoff path. Dry the sensor until it returns to dry, re-enable the closing action and press Save, then repeat the towel test. Watch the handle move, verify downstream flow stops and check the phone alert. Inspect the automation trace if a step needs attention.
• Keep it closed while you inspect. Remove the towel and dry the contacts. The dry state should leave the valve closed. Inspect the area, then deliberately reopen the valve and restore the sensor to its monitoring position.
• Repeat at each final location. Test each sensor separately, including its radio connection and the action you assigned. For the sump sensor, verify the separate alert-only recipe.

The automation editor documentation covers disabling individual actions, and the testing guide explains traces. Save the final enabled automation after the tests, with every sensor dry and reporting normally.

Give the system a little ongoing attention

Add your leak sensors and valve control to a dashboard you’ll actually open. Look at battery readings, wet/dry state and device availability. Home Assistant’s moisture trigger ignores unknown or unavailable sensors; treat those states as jobs to fix, rather than a dry reading.

The Titan’s included wired probe adds another useful layer near the actuator. Zooz says it can close the valve without the hub, and drying that probe doesn’t automatically reopen it. It still needs power. The wireless route also needs the Home Assistant host, both radios and actuator available, so plan their power together; our UPS-sizing guide helps with the host side.

Retest after moving a sensor, changing a battery or updating the control setup. Keep manual access to the shutoff clear. Once the first sensor can reliably start your tested sequence, add the next spot and repeat—the satisfying part is knowing exactly what each little puck will do when it finds water.

Find your next project on the Home Assistant hub, or return to the starter kit for the host, radio and first sensor automations.

For doors and motion, the Alarmo DIY alarm guide adds arm modes and entry delays. Keep the leak-to-shutoff automation active independently of whether your intrusion alarm is armed.

For the radio setup, our Connect ZWA-2 and Z-Wave first-device guide walks through inclusion, security keys and network backups before you add the Titan.