This water sensor module is part of the Twig system. This sensor works by having a series of exposed traces connected to ground and interlaced between the grounded traces are the sens 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. believe it or not this circuit will work with the digital I/O pins of your Arduino or you can use it with the analog pins to detect the amount of water induced contact between the grounded and sensor traces.
 

Model
Brand	Seeed Studio
Model	SEN01111P
Specifications
Description	Grove compatible interface Low power consumption 2.0cm x 2.0cm twig module High sensitivity