It's water Borewell, the depth is approx 420ft, and 6 inch diameter. I would like to know what is the water level in my Borewell and keep an eye on how much water is available etc..
If just warning point is needed, We just need a pair 315MHz/433MHz Arduino.
Plan D.
Use a pair 315MHz/433MHz Arduino, put transmitter into IP 68 enclosure and fix it on warning point . if water cover it then RF will be off, otherwise it is on.
Pro. wireless, dirty cheap, Arduino centric, few USD.
Con. only give one warning point.
B.T.W. This works better in salt water than fresh water, but fresh water should work.