SEN0308 --how "waterproof" is it?

I've used other capactive moisture sensors in the past where the sensor fails over time in cases where it is submerged in water (water level below the electronics; water only on PCB) because the PCB absorbs the water.  

Can this sensor be used as a water level sensor (as opposed to a moisture sensor)?  Do I need to  comformally coat the PCB to make it “really” waterproof?

Thank you,

Jorge