Ive done two "water" sensors in my time. First was decades ago using a CMOS quad gate, 1 gate to detect rain, 2 to make a gated multivibrator, and 1 spare.

Theory is CMOS has near infinite input resistance, so you use a megaohm pull-up resistor on the gate input, and the probe is the input and ground signals. Any liquid bridges the input pulling it to ground. I have not tested this with a PIC, but since the PIC is CMOS based I would expect this trick to still work. Even better would be to set the input as analog and use a A2D to sense (immune to half-VDD input level disasters). A baseline 10F part should work.

The next version was a continuous level sensor similar to this: http://www.innovativesensing.com/htm...ucts.asp?id=18

The probe is a tube within a tube to form a capacitor. Changing liquid heights change the dielectric which changes the capacitance linearly with level height. My "boss" used a 555 timer to convert the capacitance to a frequency, I used a PIC to measure the frequency, calibrate the levels for whatever fluid was being used, and drive the output.