# **Box  5.3 Santiago, Chile—From fear of cholera to full wastewater treatment in two decades**

In 1991, after suffering endemic typhoid over several decades, and facing the beginning of a cholera outbreak, both diseases being linked to indirect wastewater irrigation (see Box 2.7), the Government of Chile (GoC) took decisive action aimed at eliminating the hazard of using untreated wastewater and bringing these diseases under control. As a first step, the government created a National Commission to Avoid Cholera, which involved several ministries (Agriculture, Health, and Public Affairs), and put in place an emergency control program of public health interventions and sanitary education. The emergency program comprised interventions on three broad fronts:

- Improving irrigation and drinking water quality

- Changing the irrigation practices of farmers

- Changing the consumption behavior of the population

Measures to improve irrigation included the immediate construction of interceptors along some of the most polluted reaches of rivers serving as irrigation channels, and chlorination of others. Loans were offered farmers to encourage them to drill wells and provide clean water for irrigating their fields. Also, to induce famers to change their irrigation practices, the GoC banned the sale of wastewater-irrigated produce, removed this produce from the markets, and banned transportation of the produce outside Santiago metropolitan area. Banned crops included all vegetables normally consumed raw. This ban was accompanied by intensified sanitary inspection of irrigated areas, and the destruction of any banned crops that were encountered.

The most significant intervention was a Ministry of Health campaign to educate the public about the health risks of eating raw vegetables, augmented by growing press coverage about cholera and typhoid. Finally, the sale and consumption of raw vegetables and salads in restaurants was banned throughout the metropolitan area—a ban that continued for several years. For the first time, the government, the public, and the farmers worked together on a broad front to raise awareness of and resolve the problems and risks associated with using polluted rivers as a source of irrigation water.

The emergency control program was successful not only in preventing the spread of cholera into Chile, but also in controlling and reducing the rate of typhoid in the Santiago metropolitan area to unprecedented levels. Typhoid cases dropped from 3,558 average cases per year in the pre-intervention period from 1985-90 to 454 cases post-intervention in 1992. Since then, the incidence rate of typhoid in all of Chile has steadily declined from high annual rates in excess of 50 cases per 100,000 population from 1950 to 1990, to 12 cases per 100,000 population in 1993, and down to 2.2 cases per 100,000 population in 2006.

However, because the emergency program was not targeted at structural measures to control pollution from urban wastewater—but rather was aimed primarily at behavior—the sustainability and longer-term effect of these interventions was difficult to predict. Accordingly, the GoC also embarked on investing in engineering solutions. The first step was the completion of the construction of two major wastewater interceptors being financed by an existing World Bank project for Santiago Water Supply and Sewerage II. In addition, the project financed the construction of a pilot wastewater treatment plant —the first for Santiago—along with the preparation of a definitive feasibility study of wastewater treatment options for the greater Santiago metropolitan area. Early estimates of the full cost of treatment were on the order of US$78 per year, or about US$0.14 per m<sup>3</sup> , to be added to the water and sewerage tariff.

As part of an economic study of environmental issues in Chile, a policy cost-benefit analysis was carried out of the cholera emergency program implemented in 1991, and of the proposed option of full wastewater treatment. The study confirmed that compared to the risk of inaction, the emergency program yielded health benefits in excess of corresponding costs, and avoided potentially costly export losses due to inaction. Regarding wastewater treatment and indirect irrigation use, the study found that combined annual benefits of reduced or avoided mortality and morbidity due to typhoid and cholera, avoided export losses, expanded farm output, and reduced consumer costs, when added together, amounted to between $23.7 to $76.6 million annually. These benefits alone would significantly offset the annual cost of full treatment ($78 million) without considering additional benefits such as reduced mortality and morbidity due to hepatitis and diarrheal diseases beyond typhoid and cholera (estimated at between $33.4 to $166.9 million annually), amenity and other environmental values, or the value of the water use rights of treated effluent. Thus, after decades of inaction, policymakers 54