measuring water level in a waterbarrel

I would like to measure the waterlevel in a water barrel using several moisture sensors.
Each sensor would be put on a different level in the barrel (empty, 1/3, 2/3, full).
If possible the water level should be indicated on an LCD RGB backlight screen.
Can you please help me with the sketches for this?

It will be easier to measure the weight of the barrel, and calculate the water level from that.