One of the main imports into urban areas is food. At the same time, cities export daily a vast volume of wastes to be disposed of in their bioregion or in adjacent regions. Historically, these wastes have been inputs into the production of a city's food, and they can again become so. Converting food waste into fresh food reduces food costs, improves its quality, improves the environment, creates jobs, and reduces municipal management costs. The recycling of urban organic wastes is particularly critical because without it, nutrient and pathogen pollution damage health and reduce the capacity of the environment to sustain future generations.
Urban agriculture can play a significant role by recycling both waste water and solid waste.
Waste Water Cities in arid and semi-arid regions have a limited availability of water for household use and irrigation. Nutrient-rich waste water provides a precious agricultural input. Its value increases with a decreasing income level, as the potential user has less capacity to pay for organic and chemical fertilizers. Its value is also enhanced as it is available close to markets. Waste water can substitute for freshwater, which then increases the availability of freshwater for drinking, cooking, and other uses.