- In some cases untreated effluent may constitute nearly all the dry-weather flow in rivers used for irrigation, so that indirect use in reality is closer to direct reuse (e.g., Lima, Peru).

- Some countries, including some of the lower-middle-income countries, have introduced the planned use of treated wastewater, both indirect (e.g., Jordan) and direct (e.g., Tunisia).

Case studies (Boxes 2.5–2.8) show that even lower-middle-income countries can make significant improvements in wastewater irrigation schemes when driven by concerns about health, water scarcity and drought, proximity and reliability of water supply, urban food demand and food security, protection of agricultural export markets, and the pollution of critical water sources. It is apparent that the experience of epidemics or acute water shortages can contribute significantly to the formation of political resolve as a critical element to achieve improvements and to drive progress toward coherent wastewater use and water resources management policies and goals. Also, the introduction of wastewater treatment is an essential step toward achieving planned reuse. However, in most middleincome countries emerging wastewater management still coexists with extensive water pollution and wastewater reuse issues.

# **Box  2.5  Santiago, Chile—indirect use of untreated wastewater**

In 1991, the Greater Santiago urban area had a population of 4.7 million and generated 13 m<sup>3</sup> /s of domestic and industrial wastewater. The latter was projected to double over the next 30 years. The collected wastewater was discharged in more than 40 spots along three major natural river channels that drain the metropolitan area: the Mapocho River, the Maipo River, and the Zanjon de la Aguada. The resulting pollution of the three water courses in turn polluted the entire network of irrigation canals that derive from them and irrigated some 130,000 hectares of high-producing agricultural lands, including 7,000 hectares used for growing vegetable crops for raw consumption in the Santiago market. The larger area also produces 40 percent of Chile’s fruit exports, a major industry for the country, and to a lesser extent vegetable exports.

Endemic typhoid had persisted for decades in Santiago until 1991, with incidence rates in some years reaching hyper-endemic levels in excess of 150 cases per 100,000 population. Epidemiological studies linked typhoid transmission in Santiago to the indirect use of wastewater for irrigation of vegetables via the “long cycle” (infected individual → sewage → water pollution → food → people). The incidence of typhoid in Santiago far exceeded rates in the rest of Chile, and exhibited a seasonal variation with more cases in the dry summer months coinciding with irrigation and vegetable harvesting. Also, the causal agent of typhoid ( _Salmonella typhi_ ) was isolated directly from irrigation water. The appearance of cholera in Santiago in 1991, when a major cholera epidemic broke out in Latin America, raised another serious health threat to the local population since cholera is spread similar to typhoid via the “long cycle.” The cholera outbreak also posed a considerable threat to Chile’s agricultural export business that was valued at $1.1 billion annually.

How the Chilean authorities confronted and overcame these threats through decisive interventions is described in detail Box 5.3. To briefly summarize, an emergency control program was put into place to improve water quality, change irrigation practices, and change consumer behavior. This was accompanied by health education campaigns and intensive press coverage about cholera and typhoid. The emergency program achieved immediate results, and was later supplemented by development of a sanitation plan in 1998 that will be completed in 2012 when all of Santiago’s wastewater will be treated.

_Sources:_ Bartone, 1994; Ferreccio, 1995; Larrain, 2009.

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