The purpose of this concept paper isto introduce the special case of waswater-fed duckweed aquacultuie, or "aquasanitation", as a new alternative to urban and periurban water supply and sanitation indeveloping countries. Aquasanitation is a managed biological process combining the sanitary treatment of human wastes with cultivation of aquatic plants of the Lemnaceae family, the common duckweeds. Duckweed biomass and a treated effluent of better than tertiary quality are two products of the system. The final product that drives the system financially isfish. A by-product derived from drying fresh duckweed is a high protein animal feed ingredient competitive with soybean meal.