The agricultural reuse of untreated, partially treated and diluted wastewater is a common reality in and around three out of four cities in low-income countries. It is practiced in both dry and wet climates, mostly as an informal activity. In several instances, raw wastewater is used in irrigation; in the majority of the cases, however, wastewater is discharged into water bodies and thus used in diluted form. The main driving forces identified for the growth of this practice include general global scarcity of freshwater resources and contamination of water bodies traditionally used for irrigation, especially around urban centres. Estimates on the extent of this practice range widely, but figures point at about 20 million ha of land irrigated in this way, most of it in Asia, Latin America, and sub-Saharan Africa. Benefits highlighted in the cases reviewed include its reliable flow (which allows for multiple cropping across all seasons and climates), nutrient recovery, contributions to urban food supply and safeguarding of livelihoods (especially for the urban and peri-urban poor). However, health risks for farmers and consumers, such as worm infections, diarrhoea and skin diseases are major possible drawbacks, limiting formal recognition and support of wastewater irrigation. Nevertheless, low-cost interventions, as recently recommended by the World Health Organization and tested in West Africa, have shown great potential to reduce the health risks between farm and fork, especially where comprehensive wastewater treatment is not yet feasible. The development of locally appropriate risk reduction interventions should involve their users from the start in taking advantage of farmers' own innovations.

This chapter serves as an introduction to the book and provides brief information about urbanization in West Africa, and in Ghana in particular, the general role of urban agriculture and the common use of polluted irrigation water. It describes our focus on irrigated smallholder vegetable production and our understanding of the terms 'urban', 'peri-urban' and 'wastewater'. The chapter reflects on some of the key challenges of the farming system, its dynamic and resilience. It also gives an overview on the structure of the book, the origins of the data and the main objective of this publication. 1.1 The Urbanization Challenge Globally, more people are living today in urban as opposed to rural areas. In West Africa, which hosts the megacity of Lagos, the population living in urban areas has increased from only 4% in 1920 to 45% in 2011. The 50% benchmark has been passed in Ghana as in the quickly urbanizing coastal belt of West Africa, while the drier and less populated northern belt of West Africa remains so far mostly rural. For Ghana, a population split of 50.9% urban to 49.1% rural (Table 1.1) has been estimated based on the 2010 census (GSS 2012c).

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To identify interventions which reduce health risks of consumers where highly polluted irrigation water is used to irrigate vegetables in West Africa, scientists worked over 5 years with farmers, market traders and street food vendors in Ghana. The most promising low-cost interventions with high adoption potential were analyzed for their ability to reduce common levels of pathogens (counts of fecal coliforms and helminth eggs). The analysis showed the combination potential of various interventions, especially on-farm and during vegetable washing in line with the World Health Organization (WHO) guidelines. The tested market-based interventions were important to prevent new or additional contamination

Background: Wastewater irrigation for vegetable production is a highly prevalent practice in Addis Ababa and a number of articles have been published on wastewater-irrigated soils and vegetables contaminated with heavy metals. However, to the best of our knowledge, an insight into assessment of human health risks associated with the consumption of vegetable crops grown on wastewater-irrigated soils is non-existent in the city. Long-term effect of wastewater irrigation on the build-up of heavy metals in soils and selected vegetable crops in Addis Ababa urban vegetable farming sites (10) was evaluated. By calculating estimated daily intakes (EDIs) and target hazard quotients (THQs) of metals, health risk associated with the consumption of the analyzed vegetables was also evaluated. Results: The heavy metal concentrations in irrigation water and soils did not exceed the recommended maximum limits (RMLs). Moreover, Cd, Co, Cr, Cu, Ni and Zn concentrations in all analyzed vegetables were lower than the RML standards. In contrast, Pb concentrations were 1.4-3.9 times higher. Results of two way ANOVA test showed that variation in metals concentrations were significant (p < 0.001) across farming site, vegetable type and site x vegetable interaction. The EDI and THQ values showed that there would be no potential health risk to local inhabitants due to intake of individual metal if one or more of the analyzed vegetables are consumed. Furthermore, total target hazard quotients (TTHQs) for the combined metals due to all analyzed vegetables were lower than 1, suggesting no potential health risk even to highly exposed local inhabitants. Conclusions: There is a great respite that toxic metals like Pb and Cd have not posed potential health risk even after long term (more than 50 years) use of this water for irrigation. However, intermittent monitoring of the metals from irrigation water, in soil and crops may be required to follow/prevent their build-up in the food chain.

CITATIOn: Pavelic, P.; giordano, M.; Keraita, b.; Ramesh, V; Rao, T. (Eds.). 2012. groundwater availability and use in Sub-Saharan Africa: A review of 15 countries. Colombo, Sri Lanka: International Water Management Institute (IWMI). 274 p. KEyWORdS:groundwater development / groundwater potential / groundwater recharge / aquifers / groundwater irrigation / irrigated farming / groundwater policy / groundwater extraction / water availability / water storage / water quality / water use / domestic consumption / livestock / case studies / wells / boreholes / pumps /costs / drainage / socioeconomic environment / hydrogeology / legal aspects /water rights / Sub-Saharan Africa ISbn no: ISbn 978-92-9090-758-9Printing and design by dhrutidesign, India

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Background: In Addis Ababa, where irrigation water for vegetable production is commonly derived from the highly polluted Akaki river, information on microbial contamination of water and irrigated vegetable is scanty. An assessment was done to determine the microbiological quality of irrigation water and lettuce harvested from 10 urban farming sites of Addis Ababa. The efficacy of 5 lettuce washing methods were also assessed. A total of 210 lettuce and 90 irrigation water samples were analyzed for faecal coliform and helminth eggs population levels. Results: The mean faecal coliform levels of irrigation water ranged from 4.29-5.61 log 10 MPN 100 ml −1 , while on lettuce, the concentrations ranged from 3.46-5.03 log 10 MPN 100 g