Water presence sensor

Sump pump sensor. Looking for a suitable sensor for a 9v sump pump full alarm. Simple circuit. 9v battery. Sensor needs to be submersible. Found plenty of water level sensors but no simple on off. No water equals no alarm. Water to top of pump equals alarm. Any suggestions?

https://www.seeedstudio.com/Grove-Water-Sensor.html

Thank you!

I have been using simple on-off float switches to control the filling of my irrigation storage tanks for 3 years. Never had a problem. Purchased on Ebay.
Paul