It is well recognized that irrigated agriculture can play a key role in finding alternative uses for urban wastewater that is now contaminating many good quality river supplies. A key step is to understand how the wastewater can be safely used. A recent set of international guidelines has been developed by the World Health Organization (WHO) that describes the levels of treatment needed for the various agricultural-type uses. Reality is, however, that treatment facilities sufficient to meet these guidelines may be a decade or more away. As a result, the extent of water supply contamination is increasing and irrigated agriculture is now being assessed as to whether it is linked to the spread of diseases including cholera.
Interim steps need to be taken to control how irrigation water is used. Most of the focus of control has been centred on where direct wastewater irrigation occurs but there is also a need to restrict cropping in areas that have contaminated irrigation supplies. One of the limitations of such an effort is the lack of well defined health-related water quality standards for water actually used for irrigation.
This document reviews the availability of water quality standards and describes an interim approach to standards that emphasizes promotion of safe production areas for high-risk crops such as vegetables. The approach is to assess the quality of water actually being used for irrigation against a known standard. In this interim period, it is proposed to utilize the WHO Guidelines for sewage treatment plant design as irrigation water standards to make this assessment. It is recognized that these guidelines were not intended for such use and there are few, if any, data that link such standards to disease incidence. Considering that the present level of water contamination in many countries already seriously exceeds these guidelines, achieving them in vegetable production areas as an interim step would be a major step toward improving health conditions that result from irrigation practices.
Use of these guidelines is untested. Proposing them here is to begin a process of assessment and eventually working toward a slightly modified version of the guidelines. The approach described here is to utilize these interim guidelines to promote "safe production areas", not to operate a crop restriction programme.
The focus of this report is centred around procedures developed and studied in 1992 in a FAO project in Chile. Because of the concern for the spread of cholera and other diseases by irrigation practices in Chile, both the farmers and the government began an aggressive programme to assess the extent of water supply contamination and to assure the consumer that raw vegetables were being produced in a safe environment. The focus of these joint efforts was "prevention" and that focus is used throughout the document. In addition, the entire programme should be considered interim. When the proper treatment facilities for wastewater are completed such a programme can be abandoned.
It is hoped that this report will attract expert comment. Comments and suggestions for improvement of its practical application to the field would be welcomed and should be addressed to:
Chief, Water Resources, Development and Management Service
Land and Water Development Division
Food and Agriculture Organization of the United Nations
Viale delle Terme di Caracalla
00100 Rome, Italy