Most liquids have dielectric constants from 2 upwards, which makes them easy to distinquish from air,
even through the existing insulation over the wires. Water has a massive dielectric constant of 80 or
so, hydrocarbons like paraffin are around 2 and are the most demanding to detect.
[ aside - the reason ethernet cables and RF coax use polythene or teflon, not PVC, for the signal wire
insulation is to reduce moisture absorption which would otherwise cause big variations in wire dielectric
constant and thus characteristic impedance of the wire, and moisture is also a very lossy dielectric so it
would absorb higher signal frequencies more. Sometimes you don't want capacitive sensing happening! ]