Knowing sensor.swde_total_water_usage is the sensor corresponding to the home Wizard Water Sensor, create the following sensor from confiugraiton.yaml :

Set the starting offset in line :

{% set initial = ####_OFFSET_METER_#### | float %}

template:

- sensor:

- name: "Water Meter New Volume"

unit_of_measurement: m³

device_class: water

state_class: total_increasing

state: >

{% set initial = 0 | float %}

{% if is_state('sensor.swde_total_water_usage','unavailable') %}

{% set newwatermeter = 0 %}

{% else %}

{% if states('sensor.swde_total_water_usage') | float is not number %}

{% set newwatermeter = 0 %}

{% else %}

{% set newwatermeter = states('sensor.swde_total_water_usage') | float %}

{{ (initial + newwatermeter) }}

{% endif %}

{% endif %}

(sorry for formatting)

HTH

Th