ESP32 Water Leak Sensor with Home Assistant (ESPHome & MQTT) – Complete 2025 Guide

Water leak sensors can prevent serious damage from leaking pipes, washing machines, dishwashers, boilers, and under-sink plumbing.
With an ESP32 and a simple water leak probe, it is easy to build a low-cost, fast, and fully local leak detection system that integrates with Home Assistant.

This guide shows how to build an ESP32-based water leak detector using:

Simple wired probes or low-cost leak modules
ESPHome for auto-discovery
MQTT for manual integration

1. How the Water Leak Sensor Works

Most DIY water leak sensors are simple contact probes:

Two exposed metal pads or wires are placed near the floor
When water touches both, it conducts electricity
The ESP32 reads this as a digital ON/OFF signal
Home Assistant sees a binary_sensor indicating LEAK / DRY

This can trigger:

Push notifications
Sirens or buzzers
Pump shutdown
Valve closure

2. Hardware Required

ESP32 DevKit
Water leak sensor board or two stainless-steel probe wires
Jumper wires
10kΩ resistor (if using bare probes)
USB cable
(Optional) Buzzer or siren relay

Common leak sensor options:

“Rain sensor / water level detection” modules
“Water leak sensor board with 3-pin connector”
Bare probes made from stainless screw heads or copper pads on PCB

3. Wiring the ESP32 Water Leak Sensor

3.1 Using a ready-made leak sensor module (digital output)

Most modules have:

VCC (3.3V or 5V)
GND
DO – digital output, goes HIGH/LOW based on water presence

Example wiring:

ESP32 → Leak Sensor Module
3.3V  → VCC
GND   → GND
GPIO32 → DO

3.2 Using bare probes (simple DIY)

Use a pull-up resistor and read the probes as a digital input.

3.3V ── 10kΩ ── GPIO32
GPIO32 ── Probe 1
Probe 2 ── GND

When water touches Probe 1 and Probe 2, GPIO32 is pulled toward GND → leak detected.

4. Method 1 – ESPHome Integration

ESPHome makes the water leak sensor a simple binary_sensor with device_class: moisture.

4.1 ESPHome YAML for Water Leak Sensor

esphome:
  name: esp32-leak
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YOUR_WIFI"
  password: "YOUR_PASSWORD"

logger:
api:
ota:

binary_sensor:
  - platform: gpio
    name: "Kitchen Water Leak"
    pin:
      number: 32
      mode:
        input: true
        pullup: true
    device_class: moisture
    filters:
      - delayed_on: 200ms
      - delayed_off: 10s

Explanation:

pullup: true keeps the pin stable using internal pull-up
device_class: moisture shows correct icon and state in Home Assistant
delayed_on reduces false alarms due to noise or condensation
delayed_off requires a sustained dry state before clearing the alert

ESPHome devices are discovered automatically in Home Assistant.

5. Method 2 – MQTT Integration (Wired + MQTT)

For MQTT-centric setups, the ESP32 publishes "LEAK" or "DRY" to a dedicated MQTT topic.

5.1 Home Assistant `configuration.yaml` – MQTT Leak Sensor

Add under:

mqtt:
  binary_sensor:

Example configuration:

mqtt:
  binary_sensor:
    - name: "Kitchen Water Leak"
      state_topic: "home/kitchen/leak"
      payload_on: "LEAK"
      payload_off: "DRY"
      device_class: moisture

This creates a binary_sensor.kitchen_water_leak entity in Home Assistant.

6. ESP32 Arduino MQTT Code for Water Leak Sensor

The sketch below:

Connects to WiFi
Monitors the leak sensor on GPIO32
Publishes "LEAK" or "DRY" to the MQTT broker only when state changes

#include <WiFi.h>
#include <PubSubClient.h>

#define LEAK_PIN 32

#define WIFI_SSID "YOUR_WIFI"
#define WIFI_PASS "YOUR_PASSWORD"
#define MQTT_SERVER "192.168.0.10"

WiFiClient espClient;
PubSubClient client(espClient);

int lastState = -1;

void setup() {
  Serial.begin(115200);

  pinMode(LEAK_PIN, INPUT_PULLUP);

  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) delay(500);

  client.setServer(MQTT_SERVER, 1883);
}

void loop() {
  if (!client.connected()) {
    while (!client.connected()) client.connect("ESP32_Leak_Sensor");
  }

  int state = digitalRead(LEAK_PIN);  // LOW → water present (if wired to ground)

  if (state != lastState) {
    lastState = state;

    if (state == LOW)
      client.publish("home/kitchen/leak", "LEAK");
    else
      client.publish("home/kitchen/leak", "DRY");
  }

  client.loop();
  delay(100);
}

For modules where DO goes HIGH on water detection, invert the logic accordingly.

7. Dashboard Example in Home Assistant

A simple card to show leak status:

type: entities
entities:
  - entity: binary_sensor.kitchen_water_leak

Optional: add it to a dedicated “Safety” or “Alarms” dashboard with other critical sensors.

8. Example Automations

8.1 Send a critical mobile notification on leak detection

automation:
  - alias: "Kitchen Leak Alarm"
    trigger:
      - platform: state
        entity_id: binary_sensor.kitchen_water_leak
        to: "on"
    action:
      - service: notify.mobile_app
        data:
          message: "Water leak detected in the kitchen!"

8.2 Turn on a siren or buzzer

  - alias: "Leak Siren"
    trigger:
      - platform: state
        entity_id: binary_sensor.kitchen_water_leak
        to: "on"
    action:
      - service: switch.turn_on
        target:
          entity_id: switch.leak_siren

8.3 Shut off a smart valve

  - alias: "Leak Auto Shutoff"
    trigger:
      - platform: state
        entity_id: binary_sensor.kitchen_water_leak
        to: "on"
    action:
      - service: switch.turn_off
        target:
          entity_id: switch.main_water_valve

9. Recommended Installation Locations

Common places for leak sensors:

Under kitchen sinks
Under bathroom sinks
Behind dishwashers
Behind washing machines
Around boilers / water heaters
Near underfloor heating manifolds
Below fridge/freezers with water/ice connections

Probes should be:

As close to the floor as possible
Not submerged permanently, but able to touch pooled water
Protected from direct splashes that are not real leaks (e.g. from mopping)

10. Troubleshooting

Sensor always shows LEAK

Short between probes or wires
Standing water under sensor
Module adjusted too sensitively (if using adjustable board)

Sensor never detects LEAK

Probes too far apart
Surface too non-conductive (e.g. thick epoxy floor)
Poor wire connection to probes

False alarms due to humidity or condensation

Use delayed_on / delayed_off filters in ESPHome
Raise the probes slightly on a small spacer so only pooled water triggers them

11. Safety Notes

The entire detection circuit (probes, ESP32, wiring) should operate at low voltage (3.3V / 5V).
Do not run mains voltage near floor-level probes.
If controlling mains-powered valves or pumps, use isolated relays or contactors, as covered in ESP32 relay control guides.

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