Your PCB has a simple voltage comparator on it and the potentiometer is adjusted so no moisture gives a HIGH and moisture gives a LOW (or vice versa).
The conductivity of moisture/water differs too much to expect that a sensitivity adjustment can ever be accurate.
It responds to moisture or no moisture, nothing in between.
Probably in your situation, once you set the potentiometer it will not need to be readjusted ever again.
The problem with potentiometers is they are mechanical.
To prevent mechanical failure or accidental adjustment changes, you have the option of removing the potentiometer and replacing it with two fixed resistors. Obviously, no adjustment can be made if this is done.
Try the PCB as it is.
If it works and gives good results, place it in a moisture proof case to see if it works over the long term.