Abstract: A filter unit that minimizes the exposure of patients to pathogens found in the dental unit water supply lines (DUWL) while promoting frequent replacement of DUWL filters by providing a disposable microfiltration filter that is easily replaced at low cost. A disk or membrane type filter is placed in an autoclavable filter unit that attaches to the handle of an existing design dental instrument such that the form and function of the dental instrument are not adversely affected. The filter unit, which fits in-line between the dental instrument and the DUWL, includes two portions that are detachably connected by an annular sleeve. When connected, a recess between the portions forms a recess that holds a microfiltration disk filter for filtering water that flows through the dental instrument before it reaches a patient's mouth. The filter unit is easily sterilized after the disk filter is removed.