the waterlevel sensors cannot meassure that deep, only some cm
maybe some ultrasonic device would be an option?
edit - mrblonde just showed it up - the ulrasonic device from mysensors.
here’s the plugin https://www.npmjs.com/package/pimatic-mysensors
BUT as i’ve seen the ultrasonic device isn’t supported by the plugin by now.
maybe @Dheeraj can do some magic ?