Slow-sand filtration (SSF) is a tertiary treatment process that has been widely used for drinking water treatment. This technology has yet to be applied to wastewater treatment on a large scale. Pathogen reduction can be further enhanced by the addition of seeds from Moringa oleifera (a typical tree in Guatemala), which have proteins with antimicrobial properties. This project proposes to construct and operate a pilot-scale slow seed-sand filtration system at UC Davis to assess the feasibility of this technology, then to build a pilot-scale system in Sololá, Guatemala in order to adjust the system to local conditions. If successful, the pilot project will serve to encourage the community to build a full-scale treatment system.