Abstract: A filter system particularly suitable for use with a mobile floor cleaning machine. The filter system includes a first tank for receiving therein a contaminated liquid, specifically a floor cleaning liquid containing floor wax and dirt particles, and a second tank for collecting the filtered floor cleaning liquid to permit reuse thereof. The two tanks are joined by a centrifugal filter device having a rotatable filter unit which causes the contaminated liquid to flow radially outwardly through filter means which effectively removes from the liquid all solid particles except for particles of extremely small size, such as less than approximately one micron. The filter system, when mounted on a floor cleaning machine, has the first tank connected with a suction device which picks up the contaminated liquid from the floor, whereas the second tank supplies the filtered liquid to the brushes.