Dry = High Voltage / Wet = Low Voltage.
Ignore the Digital pin. Connect the Analog Out (AO) to your microcontroller. By reading the varying voltage, you can measure how hard it is raining or how wet the soil is, rather than just getting a "wet/dry" flag. Hw-133-v1.0 Datasheet
Frequently used in flight controllers and RC models where every gram matters. Dry = High Voltage / Wet = Low Voltage