In many parts of the world, good quality freshwater resources are becoming increasingly scarce. At the same time, wastewater is produced in ever-larger quantities, mainly as a result of the continued growth of the human population and the process of rapid urbanization. In reality, wastewater is a water resource of ever-growing importance, particularly for the urban and peri-urban poor whose livelihoods depend on agricultural products that can be marketed locally. However, its use for crop and fish production carries important health risks, and the disease burden that can be attributed to its unsafe use is considerable.
The World Health Organization's (WHO's) third edition of the WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater in Agriculture and Aquaculture is published in four volumes, addressing, respectively, policy and regulatory aspects, wastewater use in agriculture, wastewater and excreta use in aquaculture and excreta and greywater use in agriculture. It supersedes the second edition of the guidelines, which was published in 1989.
“This third edition of the Wastewater Guidelines marks an important departure from the previous edition,” said Susanne Weber-Mosdorf, assistant director-general for the Cluster of Sustainable Development and Healthy Environments. “The rigid and prescriptive character of the second edition has evolved to a more contemporary and flexible approach based on scientific evidence and process-oriented risk assessment and management. The Guidelines reflect a strong focus on disease prevention and public health principles. Water quality regulators will have to work towards attaining health-based targets through an integrated approach.”
Parallel to this new thinking on handling risks in an integrated manner, the guidelines also reflect new thinking in the field of sanitation. This has evolved in part in response to the sanitation target within the Millennium Development Goals. Volume 4 of this third edition elaborates on this issue and the links to safe use of excreta and greywater in agriculture.
“Eco-sanitation is scaling up from a stage of pilot studies to extensive use in a number of countries, for example China and South Africa,” said Professor Thor Axel Stenstroem, who holds positions at the Swedish Institute for Infectious Disease Control and the Stockholm Environment Institute. “Now, for the first outcomes of a recently initiated WHO/Sida study provides proof of a significantly reduced health impact. In a comparative study, the Nelson Mandela School of Medicine of the University of KwaZulu Natal (Durban) and the Ethekwini Municipality measured the incidence of diarrhoea, vomiting, skin infections and worms in six cohorts of a total of more than 7,000 people from 1,337 households. The study now provides evidence of significant correlations between disease outcome in relation to sanitation interventions, outcomes for disease per area, incidence rates of health outcome and incidence rate ratio of disease outcome.”
The guidelines clearly reflect regional differences in wastewater use and in associated public health issues. For example, the use of wastewater and excreta in aquaculture in SE Asia brings with it region-specific risks, such as the transmission of food-borne trematodes. These parasitic flukes have a complex life cycle that involves aquatic snails and fish as intermediate hosts; water bodies are contaminated by human excreta containing the parasite;s eggs. Consumption of raw or fermented fish—a common practice in rural communities of Southeast Asia—from infected ponds closes the infection cycle.
The burden of disease caused by infections with food-borne trematodes is considerable: Globally, an estimated 40 million people are at risk. Recent studies indicate that, in China alone, over the period of 1995 to 2004, the incidence of one of the various parasitic infections in this group, clonorchiasis, tripled—some 15 million Chinese were estimated to be infected with Clonorchis sinensis in 2004. A large part of this disease burden is thought to be attributable to excreta and greywater use in fishponds.
The WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater in Agriculture and Aquaculture reflect the knowledge and experience of a unique group of scientists, regulators and public health specialists brought together by the Water, Sanitation and Health Programme of the World Health Organization. The next step will be their implementation by WHO Member States. To study the obstacles and opportunities that may be encountered in their application and use, WHO and the Canadian International Development Research Centre shortly will start joint research in three countries in North and/or West Africa.