To better improve the understanding of full-scale treatment reliability and relate this to microbial control strategies, this study evaluated the particle removal performance of 67 full-scale filters and assessed the potential impact of analytical error on the uncertainty in particle removal estimates for full-scale plants. The particle removal evaluation performed in this study relied on particle count measurements as a surrogate indicator of equivalent protozoan removal performance. Implicit in these results is the assumption that the variation in treatment performance for particle removal based on particle count measures is comparable to that for protozoan removal. Includes 2 references, tables, figures.