Potable water reuse projects often use membrane bioreactors (MBRs) as part of the treatment train. MBRs offer significant footprint savings, are cost-effective, and produce high-quality effluent. However, membranes in MBRs are exposed to harsh conditions, which can result in damage, raising concerns about pathogen reduction. The determination of pathogen log reduction values (LRVs) by MBRs has been studied in Australia through the WaterVal program. The purpose of this project was to critically evaluate prior work, incorporate new data from U.S. MBR studies, propose conservative Tier 1 LRVs of 1.0 (virus) and 2.5 (protozoa), and develop a validation protocol to attain higher LRVs. The protocol developed for this project provides fundamental guidance that will assist regulators in assigning pathogen reduction credits for MBRs. Published in 2021.