Water filtration processes can reduce the asbestos fiber count in drinking water by 90 to 99.9 percent, or more. Effective fiber removal requires very close control of the treatment process. Monitoring of filtered water turbidity can indicate the efficacy of treatment, even though the asbestos fiber concentration is too low to register as turbidity. Turbidity monitoring works because when water is properly prepared for filtration, passage of asbestos fibers through the filter is indicated by the passage of floc, as shown by higher turbidity. Filtered water turbidity should be 0.10 ntu or below for best fiber removal. Continuous monitoring of each filter module at a treatment plant is recommended. These findings are based on studies at Duluth, Two Harbors, and Silver Bay on Lake Superior; Seattle's Tolt reservoir, and on data obtained from the San Francisco Bay area.