I maybe missing something in this, wouldn't be the first time. If this is just for a water level for a drinking water system, why do you need to know all of the levels? Wouldn't a high level to shut the pump off, and a low level to turn the pump on, be enough? And the easiest and least expensive way would to be to use two automotive coolant level sensors. Drill and tap a hole at both levels and insert the sensor and wire them up. Just the first one I came across that looked like it would work - http://www.fozmula.com/product/capacitance-liquid-level-switch-s87/

That sounds like an easy and inexpensive way of controlling the level on the tank. If it is a gravity feed distribution system, knowing the exact level of the tank will help in calculating the daily water demand and for leak detection.

 

If this is just for a water level for a drinking water system, why do you need to know all of the levels? Wouldn't a high level to shut the pump off, and a low level to turn the pump on, be enough?

Just minimum and maximum levels are too boring. it would be nice to know the exact water level.
Imagine a scenario, in case there is a power failure or failure of a service line (i.e unable to pump water to the tank), then it would be very informative to know the water level.... whether I could have a complete bath or run out of water

Also ,since this is a hobby project I prefer to make it . well... at least most parts of it.