Public health officials are mainly concerned with increasing deterioration of water quality due to industrial, agricultural, and urban waste and to insufficient investments in domestic water supply infrastructure. This global concern for water quality reflects the high standards imposed on drinking-water quality by institutions and professionals in the Western world, where the quality of drinking water ranks above all and where the direct use of surface water from irrigation systems for drinking seems unacceptable.

On the other hand, those who manage water for agricultural production believe their main responsibility is to provide water to meet crop-water requirements. Although few irrigation managers see supplying water for domestic use as their mandate, many rural residents draw their domestic water supply, directly or indirectly, from irrigation systems. Without acknowledging this reality, efforts to make irrigation systems more efficient might adversely affect the availability of irrigation water for nonagricultural uses. For example, lining canals with concrete to reduce seepage losses can cause shallow drinking-water wells to dry up.

The main strategy for improving rural drinking water has been to install low-cost hand pumps that draw groundwater uncontaminated by disease-causing microbes. In Bangladesh alone, more than 4 million tubewells have been installed over the past 20 years to provide safe drinking water to 95 percent of the population. This has reduced the incidence of diarrhea.

Only recently have the high concentrations of arsenic in many of the tubewells become apparent. What seemed like a public-health success story became one of the biggest environmental health crises of the 20th century—chronic poisoning of more than 20 million people exposed to high arsenic concentrations in their drinking water. A similar crisis is developing in India, where an estimated 66 million people drink groundwater with too high a fluoride content. While arsenic is toxic and carcinogenic, fluoride is an essential element for development and protection of teeth and bones. In excess, however, fluoride leads to serious dental and skeletal deformities and other health problems. Installing filters or other devices at millions of tubewells to remove arsenic and fluoride is an almost impossible task. Therefore, alternative sources of drinking water must be found in affected areas.

In some regions, the availability of shallow groundwater for drinking is an increasing problem because of overexploitation for agricultural and industrial purposes. In some of the major breadbaskets of Asia, such as the Punjab in India and the North China Plain, water tables are falling 2 to 3 meters a year. Wealthier farmers can continue to drill deeper tubewells with larger, more expensive pumps. But poor farmers are not able to do so. All stakeholders see falling groundwater levels as a threat to food security. Groundwater depletion also causes the shallow drinking-water wells of poor communities to run dry, a problem that has received less attention. Deepening these wells is costly and beyond the resources of the poor. Too little is known about how pumping groundwater for irrigation might affect the levels of arsenic and fluoride in drinking water. However, it is clear that overpumping in coastal areas causes saltwater to invade freshwater aquifers, making the water unsuitable for drinking.

The often poor water quality in tubewells and the reduced availability of water in shallow dug wells make it necessary to look at other sources of drinking water. Harvesting rainwater is being explored, but it might not be feasible in very poor arid and semiarid countries. Is reverting to the use of surface water an option when this water is increasingly polluted by human fecal material?

• Avoids direct pollution of rivers, canals, and other surface water;
• Conserves water;
• Conserves nutrients, thereby reducing the need for chemical fertilizer;
• Disposes of municipal wastewater in a low-cost, sanitary way; and
• Provides a reliable water supply to farmers.

• Health risks for the irrigators and communities in pro-longed contact with wastewater;
• Health risks for the consumers of produce irrigated with wastewater;
• Contamination of groundwater with nitrates;
• Build-up of heavy metals and other chemical pollutants in the soil;
• Creation of habitats for mosquitoes and other disease vectors; and
• Possible limiting of marketing options (particularly for export) of agricultural produce. To safeguard the health of irrigators and consumers, the World Health Organization (WHO) has formulated international guidelines on wastewater reuse in agriculture and aqua-culture. The guidelines establish the number of fecal coliform bacteria and worm eggs allowed for unrestricted irrigation.

Using wastewater for irrigation has the effect of localizing the health risk because the exposed group remains relatively small. Adequate health measures could be targeted at this exposed group. If untreated wastewater is dumped into surface-water sources, much larger populations of downstream water users could be exposed to less certain health risks. This is especially relevant for arid and semiarid countries such as Pakistan and Mexico, where irrigation canals are often the only open water bodies. These irrigation canals receive untreated wastewater from large cities, which is used for washing, bathing, and even drinking. The solution appears simple: treat the wastewater before use and disposal. Excellent treatment methods exist. But they are prohibitively expensive for most developing countries, which have the most need for this source of irrigation water. The reality today is that two-thirds of the urban wastewater generated in the world receives no treatment at all. The cost of providing wastewater treatment facilities for all cities is astronomical.

Even if the resources were available, improved water quality is not guaranteed. Many of the existing wastewater treatment plants are not functioning properly because local authorities often prefer high-technology solutions to more appropriate, lower-cost alternatives. Most conventional treatment methods remove the nutrients in wastewater, reducing economic benefits to farmers.

Restricting the type of crops being cultivated with untreated wastewater to tree or nonfood crops that pass less contamination into the food chain is another option, but difficult to enforce in many developing countries. Crop restriction also reduces economic benefits from the use of wastewater, since the vegetables most susceptible to contamination are also the most profitable.

In the foreseeable future, many towns in developing countries will continue or expand the irrigation of high-value vegetable crops with untreated wastewater. Governments may wish to regulate reuse but are unable to offer practical solutions to the users. It is urgent, therefore, to develop a framework for evaluating different options and trade-offs so that governments and communities can make better-informed decisions.

For further information see Van der Hoek, W., F. Konradsen, and W.A. Jehangir. “Domestic Use of Irrigation Water: Health Hazard or Opportunity?” International Journal of Water Resources Development, 15 (1999): 107–119.; Blumenthal, U. J., D. D. Mara, A. Peasy, G. Ruiz-Palacios, and R. Stott. “Guidelines for the Microbiological Quality of Treated Wastewater Used in Agri-culture: Recommendations for Revising WHO Guidelines.” Bulletin of the World Health Organization, 78 (2000): 1104–1116.; Shuval, H. I., A. Adin, B. Fattal, E. Rawitz, and P. Yekutiel. “Wastewater Irrigation in Developing Countries: Health Effects and Technical Solutions.” World Bank Technical Paper No. 51. Washington, D.C.: The World Bank, 1986.

Wim van der Hoek (w.van-der-hoek@cgiar.org) is the leader of the Water, Health, and Environment Theme at the International Water Management Institute, Colombo, Sri Lanka.