Impact of municipal wastewater use on urban and peri‑urban agricultural productivity: the endogenous treatment-effects approach

• There is an observed positive selection on value of vegetable output gains from the use of municipal wastewater. • Extension availability decreases the use of municipal wastewater for vegetable production • Extension service plays an important negative mediation role in the treatment effect of municipal wastewater use on vegetable productivity • Vegetable productivity returns to use of municipal wastewaters tends to be heterogenous when extension contact is established. • The study recommends the supply of affordable but efficient small-scale wastewater filters to promote safer use of municipal wastewaters and enhance sustainability of urban agriculture. Current trends in urbanization and climate change in many arid and semi-arid countries across sub-Saharan Africa are threatening the sustainability of Urban and Peri-urban Agriculture (UPA) and food systems due to rapidly growing competition for scarce resources such as water and land. Water scarcity in the sub-region is currently recognized as a multidimensional problem, affecting urban farm productivity, food safety, food security and poverty, as well as public health systems. The use of treated or untreated municipal wastewater (MWW) in agriculture has increasingly become a relevant option for freshwater conservation, optimizing the agronomic and economic gains, and increasing urban food security and nutrition. This study investigates empirically the link between MWW use and productivity of vegetable farmers in Ouagadougou, Burkina Faso. Using survey data from 416 vegetable farmers, we employed a semi-log production function augmented with an endogenous binary-treatment effect equation to estimate the drivers and impact of MWW use on value of vegetable output, accounting for selection bias and omitted variable problem. We find that MWW use alone is associated with higher value of vegetable output. However, regulation through contacts with extension agents reduces the agronomic and economic benefits of using MWW for irrigation. This study proposes a provision of small but efficient wastewater treatment technologies with the support of extension agents and a redesign of extension education that promotes safer MWW use to maximize its productivity benefits for all farmers. We also suggest that future research should explore the long-term impact of MWW use on soil health and the effect of extension education content and mode of delivery on vegetable production.