Finding the home site (given on the back of the sensor!), www.robotbase.cn
, it was possible to find better
pictures of the board (both sides).
Its wired like a phototransistor(!) to + and - pins only. The leakage current from the traces goes to the base of
the transistor - without current limiting its going to be very easy to burn out the transistor.
You should put a 1k resistor from the + pin to a digital pin, wire - to ground, ignore the S pin (its assuming
standard 3-wire servo connectors). Then take the + pin also to an analog input.
To use drive the digital pin high to energize, read the analog level, then remove the drive to the digital
pin (this stops you being electrolysing the water and corroding the sensor away).
Its sensitivity will depend very strongly on the ionic concentration of the water sampled, note.