摘要：Irrigation with raw or diluted wastewater is a widespread phenomenon, occurring on 20 million hectares across the developing world, especially in Asian countries, but also in peri-urban areas around almost every city of sub-Saharan Africa and in many Latin American cities. Growing urban populations and consequent increases in demand for food and water has spurred the use of sewage to water crops as this is, in many cases, the only form of irrigation for farmers who either lack clean water or for whom clean water is too expensive. Wastewater has high nutrient value and constitutes a reliable source (Scott et al., 2004). It is mostly used to produce cash crops (e.g. vegetables and cereals). For example, it has been estimated that in most parts of Sub- Saharan Africa, urban and peri-urban farms irrigated with polluted water resources contribute 60-100 percent of the vegetables needed in most cities (IFPRI, 2008). Production of these cash crops is found to generate significant livelihood opportunities, not only for urban and peri-urban farmers but also for traders, input suppliers and other service providers (Scott et al., 2004; Water Policy Briefing, 2006).
