My Mom is increasingly forgetting to turn off the faucet in her bathroom sink and we wake up before her in the morning to discover it has been running for who knows how many hours.
Is there a sensor I can purchase which will work with HA to send a notification if the water has been running for more than a set period?
I don’t want to have to DIY the hardware if possible.
Thanks
You don’t mention where your mom lives, but in the United States Flume (flumewater.com) sells a device that is fairly easy to install and works well. It will notify you of high usage directly without HA but also has an integration. In some cases the purchase will be credited by your local water utility.
I have a none-specific solution: a water pulse meter on my main entry and a esp/wemos.
This does not measure an individual use of course, but it can detect a longer use of ‘water’, which can be shower, washing machine, etc.
With some 'logic you could tweak this to: if usage more than (say) 10m > alert
Of course you can install a simiilar solution for the particular faucet but effort/cost <> gain (your decision)
In the US and I will look up Flume and other whole house solutions.
I was also thinking of replacing the faucet with something that will auto shutoff after a while or if presence is not detected or something.
alos this works for me:
I’m always willing to try new things even if I end up regretting the time and energy I put into it 
Does one have to do anything to configure the USB dongle in HA beyond the mqtt section in configuration.yaml?
Is LIBRTL something I have to run on a separate docker host running in parallel to HA which I have running as a standalone VM?
P.S.: I have a smart meter for gas and electricity but not sure I have one for water. I should probably check with my water company first!
2 additional Docker containers are required @unmesh59 - rtl_sdr (decrypts radio stream and streams it to a port) and metermon (reads rtl_sdr port and sends mqtt). I run these 2 containers on HA docker instance (HA complains about this in health status but having other containers never caused any issues for me in several years of running it).
No other cfg needed in HA - just MQTT sensors.
Sounds good though I just learned that our water company has not yet begun installing smart meters