Monitor home water usage in Home Assistant using RTL-SDR

An work-in-progress solution for monitoring water usage in Home Assistant using an RTL-SDR and a Raspberry Pi. This functionally captures the reading of my Neptune E-Coder R900i water meter in Saint Paul, MN and should work and should work for every home in this city. YMMV in other locations or with other meters.

Using a Nooelec RTL-SDR v5 and a Raspberry Pi, one can wirelessly capture the same unencrypted water meter readings that the city uses for billing.

Prerequisites

I have this running on Debian on a Raspberry Pi 4B. The compute demands of this are minimal and this could certainly run on less powerful hardware.
Build rtl-sdr from source. I found this to be a bit tricky, these instructions helped.
Install Go. I had issues with the apt package and found that downloading and installing the binary directly worked best.
Install jq to transform rtl output into JSON understandable by Home Assistant:
- sudo apt install -y jq
Install stdout_httpd and rtlamr
- go install github.com/abaker/stdout_httpd@latest
- go install github.com/bemasher/rtlamr@latest

Listen for broadcasted events

With rtl-tcp running, have rtlamr listen for message type r900 on frequency 912 Mhz. Filter out the noise of your neighbor's meters by using the serial number displayed on top of the meter, below the display.

./go/bin/rtlamr -msgtype=r900 -centerfreq=912000000 -filterid=WATER_METER_SERIAL_NUMBER

Once you are successfully reading the meter, edit watermeter.sh to include your serial number. If you are not seeing a reading, you can force a updated reading by turning on the faucet. New readings are normally broadcast roughly once per minute.

The script will automatically run the required software, and publish the required information in JSON on port 8080. Example output:

{
  "Time": "2023-07-17T01:21:13.591313046+01:00",
  "Offset": 0,
  "Length": 0,
  "Type": "R900",
  "ID": WATER_METER_SERIAL_NUMBER,
  "Unkn1": 163,
  "NoUse": 0,
  "BackFlow": 0,
  "Consumption": 6162823,
  "Unkn3": 0,
  "Leak": 1,
  "LeakNow": 0
}

Run automatically

The script can be set to run automatically at startup or after a crash (RTL-SDR adapter can be somewhat unreliable) by following the instructions commented in watermeter.service

Configuration in Home Assistant

Once configured, the readings can be input in Home Assistant using a REST integration.

Add the following to your configuration.yaml:

  - platform: rest
    name: Water Meter (gal)
    resource: http://IP_ADDRESS_OF_RASPBERRYPI:8080
    force_update: true
    value_template: "{{ value_json.Consumption | float / 100 * 7.48 | round }}"
    unit_of_measurement: "gal"
    device_class: water
    state_class: total_increasing
    json_attributes:
      - Time
      - BackFlow
      - Consumption
      - Leak
      - LeakNow

Note that the R900i meter reports readings in cubic yards. The Consumption variable also leaves out the decimal place. For example, the output in the example above is actually 61,628.23 yd^3. This is adjusted with value_template: ... float / 100 ...

This isn't a super useful unit for me to measure day-to-day water usage in, so I convert it to gallons in value_template. Update accordingly based on your preferred units.

After a restart, the water meter entity should begin populating. Water meter can be read added to the Energy tab for a nice visualization of your resource usage:

Future improvements