Measuring Water Level in a Tank Using ESPHome and Home Assistant

Do you need to keep track of how much water is in your tank? In this guide, I’ll walk you through how I built a simple water level sensor using:

• 🧠 ESP32
• 📏 AJ-SR04M waterproof ultrasonic sensor
• 💡 ESPHome
• 🏠 Home Assistant

With this setup, I can now see the tank level as a percentage and in liters, and even get a notification when the water is low.

🧩 Hardware Used

• ESP32 Dev Board
• AJ-SR04M waterproof ultrasonic sensor (4-pin version: VCC, GND, Trig, Echo)
• A couple of resistors (1.8kΩ and 3.3kΩ for a voltage divider)
• Dupont cables and a power source (USB or 5V supply)

⚡ Wiring the AJ-SR04M to the ESP32

Since the Echo pin outputs 5V, you need to use a voltage divider to drop it to ~3.3V to avoid damaging the ESP32.

Voltage divider circuit:

• Echo → 1.8kΩ → ESP32 GPIO22
• Same point → 3.3kΩ → GND

🧠 ESPHome Configuration

Here’s the YAML I used in ESPHome:

esphome:
  name: water_level_sensor
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "your_wifi"
  password: "your_password"

logger:
api:
ota:

esp32_ble_tracker:
bluetooth_proxy:
  active: true

sensor:
  - platform: ultrasonic
    trigger_pin: GPIO23
    echo_pin: GPIO22
    name: "Water Tank Distance"
    id: water_tank_distance
    update_interval: 60s
    timeout: 4.0m
    unit_of_measurement: "m"
    accuracy_decimals: 2

This publishes the distance from the sensor to the water surface to Home Assistant.

📊 Creating Calculated Sensors in Home Assistant

My tank is 38 cm deep and holds 30 liters. Based on the raw distance, I created two template sensors in Home Assistant: percentage full and liters of water remaining.

Add this to configuration.yaml or create helpers via the UI:

template:
  - sensor:
      - name: "Water Level Percent"
        unit_of_measurement: "%"
        state: >
          {% set depth = 0.38 %}
          {% set distance = states('sensor.water_level_sensor_water_tank_distance') | float(0) %}
          {% set percent = ((depth - distance) / depth * 100) %}
          {{ [percent | round(0), 0] | max }}

      - name: "Water Volume Liters"
        unit_of_measurement: "L"
        state: >
          {% set depth = 0.38 %}
          {% set volume = 30 %}
          {% set distance = states('sensor.water_level_sensor_water_tank_distance') | float(0) %}
          {% set level = ((depth - distance) / depth) %}
          {% set liters = level * volume %}
          {{ [liters | round(1), 0] | max }}

🔔 Optional: Notification When Water Is Low

Set up an automation to notify you if the water drops below 5 liters:

alias: "Notify: Low Water Level"
trigger:
  - platform: numeric_state
    entity_id: sensor.water_volume_liters
    below: 5
action:
  - service: notify.mobile_app_yourdevice
    data:
      message: "Warning: water tank is below 5L!"

📱 Dashboard Display

Add a simple gauge to your Lovelace dashboard:

type: gauge
entity: sensor.water_level_percent
min: 0
max: 100
severity:
  green: 50
  yellow: 20
  red: 10

🧼 Results

With this setup:

• I can monitor the water level in real-time.
• I get alerts before the tank runs dry.

This is a small but practical DIY project that’s perfect for rainwater tanks, toilet water tanks, livestock waterers, or just keeping an eye on that water butt in the garden.