Abstract: A prefilter for an EDM machine includes a tank for holding flush water with guide rollers and channels used to thread a continuous sheet of filter paper along the bottom thereof such that the flush water is prefiltered by the continuous sheet filter paper. A float switch detects the level of flush water in the tank so that as the filter paper becomes clogged, it actuates a take-up motor for advancing the filter paper through the tank to remove clogged filter paper therefrom and replace it with fresh filter paper. The prefilter may be used as a kit for retrofit to existing EDM machines or provided as part of an original equipment design.