I have two fountains and each one needs to be refilled at least once a day. I thought that it would be good if I could put a flow meter on the PVC pipe in the fountain. If I could detect when the flow rate dropped to a certain point that would tell me that I need to activate a water valve to add water to the fountain. Once the flow rate got back up I could turn off the valve. I have yet to find an obvious device choice for this. For me, I need the device to be not much bigger than the PVC pipe it connects to (3/4" or 1"). And since it would be mounted inside the fountain battery power would not be an option.
It outputs pulses which the rate of pulses/minute/second can be counted by Tasmota and then sent to HE for determination.
I think Dan's Hubduino firmware for nodemcu's supports pulse counting but couldn't find a reference. You might want to post on his thread if you want and this idea is of interest.
Here's a couple of examples (not HE specific though).