Capacitance to Voltage converter - Water level sensor
An oscillator can be fashioned from the capacitor, and it is simple
to either count the frequency, or convert to a controlled current.
By DC-blocking the electrodes with C2, corrosion should be  minimal.







simulate this circuit &ndash; Schematic created using CircuitLab

The NOT inverters are 74HC14  Schmitt inverter sections, intended to be powered either from 5V, or the emitter of Q1.   If the ammeter isn't of the moving-needle type, some filtering will be required.   R2 * Csense
should be larger than R3 * C3.

I've used this circuit with a shielded cable from the Q1 emitter,
so the oscillator can be adjacent to the sense capacitor, but the
power supply and meter at a more convenient location.