Water leak sensors for Home Assistant: Zigbee and Z-Wave

A leak sensor is the cheapest insurance in a smart home. It sits on the floor, does nothing for years, and then tells you the water heater let go before the floor soaks through. The protocol you pick should match the radio you already run, not the other way around.

If you run Zigbee, Aqara and ThirdReality both pair directly with Zigbee2MQTT and ZHA. If you run Z-Wave, the Zooz ZSE42 joins your existing mesh. Either way, Home Assistant gets a moisture entity you can build a notification on.

I don’t have years on any of these in my own house, so this is a researched list, not an ownership report. Picks come from the makers’ spec pages and the Zigbee2MQTT device database.

Where to put them

Under every sink, behind each toilet, next to the water heater, under the dishwasher and fridge if they have a water line, by the washing machine, and next to the HVAC condensate drain or sump if you have one. Leaks start at connections and appliances, so that’s where the sensors go.

What to watch out for

A notification only helps if someone sees it. Send a critical alert that gets past do-not-disturb, and pick a sensor with a built-in alarm, like the ThirdReality, for spots where nobody checks their phone.

Coin cell sensors go quiet when the battery dies, and a dead leak sensor looks exactly like a dry floor. Put the battery level of every leak sensor on a dashboard or in a weekly low-battery report.

The ZSE42 handles a splash, but Zooz says it can’t be submerged. It’s built to sit on a floor and catch the first water, not to live in a sump pit.

The ZAC36 needs room around the valve: about 3 in on each side of the valve center and 1 in between the pipe and the wall. Measure your main shutoff before you buy one.

Verdict

Put the Aqara sensor everywhere if you’re on Zigbee, and add a ThirdReality wherever a local alarm would help. Use the Zooz ZSE42 if your house runs Z-Wave. If you want the house to stop a leak instead of just reporting it, add the Zooz ZAC36 on the main shutoff and wire its probe next to the water heater.