All compressors suck moisture from the air and transform it into liquid inside the tank, this is the reason why all tanks have a water bleeding/draining valve, at the very bottom of the tank, (air reservoir).
This water has to be drained regularly, more if you are in humid locations.
When the water reaches a certain volume, it is pushed into the hoses and comes out at the end as a spray. If the compressor has a good water filter, no water should pass that filter but condensation can build inside the hoses and be pushed out when air is used, this is why, for painting or use of a spray gun, another quality filter should be as close as possible to the spray gun however, the compressors should be drained regularly to void excessive water inside the main tank...!
Cheers
George