How's the Weather in Your Pipes?
What are the conditions inside your pipes, is it cloudy and hot with showers or cool and dry? Could there be snow and blowing snow and excessive icing conditions? Are there smog and dust storm conditions or is the air as fresh as a mountain breeze. All these conditions are commonly experienced inside compressed air systems. What you get is determined by your selection of system equipment, ambient conditions and how well your system is maintained. 

Why Does Compressed Air Need Drying? 
All atmospheric air contains some water vapor which will begin to condense into liquid water when the air in a compressed air system cools to the saturation point, i.e., the point where it can hold no more water vapor. The temperature at which this happens is known as the dew point. This dew point is a key factor in determining how much drying is needed. Condensation in the compressed air system would occur at the intake air saturation temperature (the dew point of the ambient air) if the temperature remained constant as air was compressed