4 Simple Water Activated Relay

The circuit uses transistors formed in a high gain (Darlington pair) configuration. When the plate is wet, transistors Q1 and Q2 turn on and activate the relay.
Water Activated relay Schematic
Part List:
R1 - 2.7 kilo ohms 1/4W
R2 - 1 kilo ohms 1/4W
D1 - 1N4148, 1N4001 or similar diode
Q1, Q2 - 2N2222, 9013 or similar NPN transistor 
RLY - any 4V to 6V relay.
TOUCH PLATE - conductors separated few mm apart
NPN transistor pinout