The use of contaminated water in high speed handpieces and ultrasonic handpieces presents potential hazards to both dentist and patient. This study has shown that after waterline sterilization, the use of a sterile, disposable membrane filter can eliminate the microflora from the water of an ultrasonic scaler for up to 48 hours. Similarly, the water from a high speed handpiece can remain bacteria free for up to 72 hours when a 0.45 micrometer pore size membrane filter is installed into the waterline. This system of decontamination by filtration may present a workable approach to the problem of contaminated water and merits further research and development. Commercial materials and equipment are identified in this report to specify the investigative procedures. Such identification does not simply recommendation or endorsement or that the materials and equipment are necessarily the best available for the purpose. Furthermore, the opinions expressed herein are those of the authors and are not to be construed as those of the Army Medical Department.