I meant to add this,

Google "Franzinator" to find out how to build a quick and dirty water separator for your air compressor (and given the state of things, put you on a list with DHS for buying pipe bomb materials).

You can also Google "Desiccant Air Dryer" and find ways to either build a smallish desiccant air dryer for your plasma cutter, or buy one cheap (under $100). Presuming the bought units are serviceable, you can regenerate the desiccant once it turns pink.