I use a desiccant cartridge filter and so far (3 years) it has worked just fine. I see no evidence of moisture in the drop just before the my mill, and have never found any in the regulator/coalescer that came mounted to the machine. In my case (prototyping) I only need to regenerate the desiccant about once every 2-3 months. The one I have is a CamAir CT30, it holds a 10 lbs desiccant cartridge. I searched around and found it new for about $200. Replacement cartridges are around $50 but so far I have been able to just regenerate mine.