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