Thanks oepi-loepi!
I'm not using that add-on, but it contains the URL where the information is pulled from:
http://toon/hdrv_zwave?action=getDevices.json
Variables are "CurrentWaterQuantity" and "CurrentWaterFlow".
According to code the quantity is in liters, but if I leave the tap open for half a minute it doesn't increase. Maybe unit is 10l or maybe my analog sensor is not reading correctly. Anyway, I'm a big step closer
SensorEntityDescription(
key="waterquantity",
name="P1 waterquantity",
icon="mdi:water",
native_unit_of_measurement=UnitOfVolume.LITERS,
device_class=SensorDeviceClass.WATER,
state_class=SensorStateClass.TOTAL_INCREASING,
),
SensorEntityDescription(
key="waterflow",
name="P1 waterflow",
icon="mdi:water-pump",
unit_of_measurement = "l/m",
device_class=SensorDeviceClass.WATER,
state_class=SensorStateClass.MEASUREMENT,
)