[prairieschooner]

I am with you Richard, not sure that a water separator is that valuable since the air needs to cool off before the Water will come out of the compressed air, this makes an external air compressor much more desirable in my mind.
When I was in the industry I used to make water traps by having larger pipe installed vertically in the air line run. The pipe would have a Petcock to allow drainage, surprising how much moisture can get collected. When moisture could become a real issue then refrigerated and/or desiccant dryers were used but then lubrication would become a problem.