My guess is that the 3 pin package is an NPN transistor, type S8050 with "J3Y" marking, with the base connected to one set of traces. One or the other of the parts should be a high value resistor, but I can't make out the markings.
You could easily verify or disprove that with a multimeter. Only $0.29 at AliExpress!
Guess at the circuit, from the description on the "best data sheet" (water on the traces effectively shorts the base to ground, cutting off the transistor):
Hmmm, I was looking at images of a different version of the sensor board. There is an LED on the one posted in reply #10, but not on the one I looked at most closely (similar to the "best data sheet" board linked in the OP).
I agree with the general circuit tracing for the image in reply #10, except for the missing LED and the stated values for the resistors.
The markings on the resistors can be read on the image posted in reply #10, and they are clearly 101, 101 and 102, which correspond to 100, 100 and 1000 Ohms, with the 1K Ohm resistor being a current limit resistor for the LED (board powered on).
If that is the board you have, then yes, as water allows current to flow to the base, the signal voltage should rise due to increased emitter current.