Because disease pandemics can accelerate rapidly in areas with limited clean-water access, a portable greywater reuse system may be useful to provide wash water at emergency health care units. In this study, a novel fed-batch (hybrid continuous-batch flow) net-zero water (NZW), or nearly closed-loop, reuse system comprising screening, 5 μm filter, and ozone-UV advanced oxidation was designed, constructed, and tested for performance with simulated and actual human showers. Water quality was tested for compliance with US drinking water standards, total organic carbon < 0.5 mg/L, and pathogen inactivation including 12 log10 virus, 10 log10 protozoa, and 9 log10 bacteria as has been recommended for direct potable reuse. Energy, operation, and maintenance requirements were also evaluated, along with the system's capacity to handle shock events such as unintentional contamination with urine. Design goals were achieved without the addition of GAC point-of-use filter, except compliance with bromate and nitrate drinking water standards, which were met only for temporary use of up to three years per person. A capacity of 32 showers/day at 1920 W continuous power is projected, without generation of potentially-infectious concentrate. To avoid the further increase in system weight and energy demand needed to address urine input, future integrated urine diversion and collection, and system drain-and-fill following detection of urine in recycled water by electrical conductivity, are suggested for the field unit. Field testing is recommended. Further research should focus on potential need for bromate/nitrate mitigation, and longer-term study of microbiological inactivation.