Water level detection using non contact sonic sensors
The easiest way to get started is to cobble a proof of concept (PoC) system out of consumer audio speakers, amplifiers, microphones.

To rephrase what you want to do: send a sound pulse from the top of long and narrow well, the pulse would travel down the well, reflect from the water level, calculate the distance to water from the round trip time of flight.

It's challenging - if at all possible - to make this work in a thin and narrow wells.  The challenge is that the sought reflection from the surface of the water will be neither first nor the last reflection you receive.  The sound will not travel in a narrow beam like a laser.  It will propagate as a cone.  At some point, this cone will become wider than the diameter of the well.   Some sound is going to reflect back from the walls, and that's going to be the first reflection you receive.  You will continue to receive reflections.  At some point, you will receive the reflection from the water at the bottom of the well.  The reflections will not stop there.  You will continue to receive multipath reflections.

Record echoes from well with known diameter and water level.  Maybe there will be a consistent feature in the echos which you can clearly identify as the water surface.  Maybe you'll see more if get several echoes at several frequencies from the same well.

p.s.  If the wells are always straight, a laser rangefinder might work.