variable voltage divider using transistors
This might be a better solution:

I have drawn only 3 sections but you can make more if you like.

You do have to change the value of the 3 k ohm resistors to

number of sections x 1 k ohm 

The 1 kohm is R10 on the bottom right.







simulate this circuit &ndash; Schematic created using CircuitLab

When the water reaches all contacts the output voltage will be about Vcc/2
If you want to have a different value change R10.

Note that the water must also be in constant contact with the ground of this circuit. And that's also how you can test that it works, just connect  the contacts to ground to simulate that they're in the water.

Circuit description: poor man's resistor-DAC, it sums the current from each section into R10.