The Pi Supply Octopus Rain/Steam Sensor can be connected to the Arduino IO Expansion shield directly. The output voltage will increase when the humidity of the sensor surface goes up. You can even use it as a touch panel.
Pi Supply Octopus Electronic Bricks can be used to build electronics projects just as easy as piling bricks. You can also connect Arduino compatible boards easily with various digital, analog and I2C/Uart interfaces. The breadboardless connections let you connect expansion modules like potentiometers, sensors, relays, servos, buttons in a plug and play way.
Warning: The connector is not waterproof. Please be careful not to put the connector directly in water.