Guidelines for the safe use of wastewater, excreta and greywater — Volume 4: Excreta and greywater use in agriculture
About this book
Guidelines for the Safe Use of Wastewater, Excreta and Greywater — Volume 4: Excreta and Greywater Use in Agriculture, published by the World Health Organization (WHO) in 2006, is the fourth volume of the most comprehensive international framework for managing the health risks associated with the use of human excreta and domestic wastewater in agricultural production. Developed through a lengthy consultation process involving 145 experts from 35 countries, these guidelines represent an evolution from earlier WHO standards toward a risk-benefit framework that recognises the legitimate role of wastewater reuse in food production, particularly in water-scarce regions. The document establishes a fundamental conceptual shift: rather than setting uniform wastewater quality standards that are unachievable in low- and middle-income country contexts, Volume 4 adopts a health-based targets (HBT) approach.
This approach defines acceptable levels of health risk — typically expressed as a tolerable burden of disease in disability-adjusted life years (DALYs) lost per person per year — and then identifies multiple barrier options (wastewater treatment, agronomic controls, food safety measures, personal protective equipment, and exposure limitation) that can be combined to achieve the target, giving flexibility based on local capacity and resources. The epidemiological evidence on disease risks associated with wastewater-irrigated food crops is reviewed comprehensively. Particular attention is given to helminths (intestinal worms such as Ascaris, hookworm, and Trichuris), which are the most significant health risk from wastewater use in agriculture in developing country contexts, as well as to enteric pathogens including Salmonella, cholera, E. coli, and enteric viruses.
The document reviews Quantitative Microbial Risk Assessment (QMRA) methodology for translating pathogen concentrations in irrigation water into disease burden estimates. Agronomic and exposure-reduction measures are given substantial coverage. The choice of irrigation method (drip versus flood versus sprinkler), the selection of crops (root versus leaf versus sub-surface crops), the timing of irrigation relative to harvest, and post-harvest handling practices are all shown to have significant impacts on consumer exposure, allowing substantial risk reduction without requiring high levels of wastewater treatment.
Volume 4 is widely applied in low- and middle-income countries where treated wastewater reuse for food production is a practical necessity, and has influenced national guidelines in India, Jordan, Mexico, Tunisia, and Ghana.