A NEW Crowtail sensor called crowtail-water sensor, it has a specific crowtail interface that compatible with crowtail base board. The water sensor detects water by having a series of exposed traces connected to ground and interlaced between the grounded traces are the sensor traces. The sensor traces have a weak pull-up resistor of 1 MΩ. The resistor will pull the sensor trace value high until a drop of water shorts the sensor trace to the grounded trace. With the digital I/O pins of Crowduino , you can detect the amount of water induced contact between the grounded and sensor traces.