The heart of this project is using PIC16F88 to determine the water level by calculate the relation of water level and the water capacitance.A simple probe can be made using insulated wire. The insulation is then the dielectric of an cylindrical capacitor with the inner conductor as one plate and the water as the other. The probe is not suitable for distilled or very pure water because it is not conductive enough. It works well even in relatively clean water such as roof runoff water in a plastic tank.
Weller WESD51 Digital Soldering Station