From Removal to Reliability: A New Perspective on Membrane-Based Virus Control in Household Water Treatment

Membrane-based household water treatment (HWT) systems are increasingly promoted for the decentralized control of microbial contamination, including enteric viruses. However, virus removal is still typically evaluated using nominal pore size and the average log reduction value (LRV) obtained under controlled laboratory conditions. In household use, membranes are typically subjected to intermittent operation, hydraulic fluctuations, variable feedwater quality, fouling evolution, and inconsistent maintenance. From a reliability perspective, virus retention can be viewed as three interacting contributions: structural retention, interaction-mediated retention, and fouling-mediated retention, each of which may change under operating conditions. We therefore propose a reliability-centered framework that distinguishes removal capacity from virus protection reliability and evaluates performance as a time-dependent reliability profile rather than a single or average LRV. The framework introduces measurable indicators, including threshold compliance, minimum LRV, breakthrough frequency, magnitude and duration, recovery, and protective service life. It also distinguishes transient transport-mediated breakthrough, in which process disruption temporarily increases virus passage without permanent membrane damage, from integrity-mediated failure, in which physical deterioration of the membrane barrier causes a more persistent loss of protection. This framework provides a basis for evaluating how consistently and for how long membrane-based HWT systems sustain protective viral removal.