In 2006 the WHO issued new guidelines which consider addressing wastewater use issues as only one component of an integrated risk management strategy (WHO, 2006). The 2006 Guidelines now include health-based targets, which correspond to the ‘tolerable’ burden of disease that would result from agricultural wastewater use. Models were used to calculate the required levels of pathogen reduction to meet the targets for different types of irrigation scenarios and employing different degrees of wastewater treatment and/or even non-treatment options. For different health protection control measures, their potential to reduce the amount of pathogens on the crop has been determined. In this way, it is possible to predict the pathogen reductions achievable with each combination of different health protection control measures, and risk management strategies can be chosen based on the targeted pathogen removal. The 2006 Guidelines are intended to provide a framework that supports the establishment of national standards and regulations for agricultural wastewater use that can be readily implemented and enforced.<sup>2</sup> Initial applications of the new framework have been made, but the approach needs to be disseminated more widely. This paper hopes to contribute to this effort.

The paper, which is based on Economic and Sector Work carried out in the Water Anchor of the World Bank, aims to highlight the growing importance of improving wastewater use in agriculture across the spectrum from lower- to high-income countries. It presents an innovative approach linking key issues related to different aspects of wastewater irrigation to a country’s level of economic development. Based on data presented in the World Bank’s World Development Report (World Bank 2010), it differentiates between four country income levels (lower-income, lower-middle income, upper-middle income, and high-income) to create a typology for analyzing current issues, trends, and priorities for improving agricultural wastewater use with a focus on reducing the risks to public health. It also presents the basic principles of the new 2006 WHO Guidelines, and how to apply them. Beyond regulatory aspects, the paper also discusses the other aspects that are important for achieving a more integrated approach to agricultural wastewater use, including institutional/planning, technological, economic/financial, and social issues. Finally, the paper provides recommendations for moving the wastewater irrigation agenda forward. The primary audiences for the paper are water professionals, regulators and decision-makers who help to plan and implement projects for wastewater use in agriculture and to develop a coherent policy and regulatory framework for such activities.

The report is organized as follows: Key issues and trends in wastewater use in agriculture are discussed in chapter 2, supported by the introduction and application of the country typology based levels of economic development. Chapter 3 reviews the benefits and risks of wastewater irrigation, with the main risk being the microbial risk to public health. The microbial risk assessment and management framework of the 2006 WHO Guidelines is discussed in Chapter 4. Based on that, Chapter 5 discusses implementation measures for reducing public health risks, and broader issues for achieving a more integrated approach to planned wastewater use for irrigation and to urban water management. Finally, Chapter 6 summarizes the key messages of the paper and discusses how countries can tailor wastewater interventions to fit their unique circumstances.

> 2 Although outside of the scope of this paper, it should be noted that the framework proposed by WHO for wastewater use in aquaculture is similar to that for wastewater use in agriculture (WHO, 2006).

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