I made this to mount in my sump pump to warn me if the water gets too high. It could be used for any similar application. I used a 3/8" magnetic reed switch along with Home Assistant (via ESPHome monitoring the reed switch) to alert me if the water gets too high.

Two mount versions are included. One is concave to fit a 1.5" PVC pipe, the other is flat.

Reed Switch I'm using - https://www.amazon.com/Yootop-Recessed-Security-Magnetic-Contact/dp/B07G78WJWK/ref=sr_1_5?crid=1A5IK9A5ZX5DI&keywords=magnetic+door+sensor&qid=1648526114&s=electronics&sprefix=magnetic+door+sensor%2Celectronics%2C75&sr=1-5