Simple water detector

This simple water detector circuit uses alternative voltage in order to prevent the corrosion of the electrodes. It is easy to build and uses N1 as a trigger Schmitt gate which generate the AC. If between the electrodes is a electricity conductor, for example an aqueous solution, then because of the rectification action of D1 and D2, the C4 capacitor is charging.
When the capacitor voltage reaches switching threshold of the N2 trigger Schmitt, the relay will trigger and connect, for example a drain pump. The pump will be disconnected as soon as the electrodes won’t touch the liquid.

Water detector components
R1 = 470K
R2 = 10M … 22M
C1 … C4 = 2.2nF
N1, N2 = 1/2 4093
D1 … D3 = 1N4148
T1 = pnp transistor (BC557)