2 Tropical Source Water Terry C. Hazen 1,2 and Gary A. Toranzos 2 'Environmental Sciences Division, Savannah River Laboratory, Westinghouse Savannah River Company, Aiken, South Carolina and 2Microbial Ecology Laboratory, Department of Biology, University of Puerto Rico, Rio Piedras, Puerto Rico Over 2 billion people, or half of the world's population, have suffered from diseases due to drinking polluted waters (Barabas, 1986). More than 250 mil- lion new cases of waterborne disease are reported each year, resulting in more than 10 million deaths and nearly 75% of these waterborne disease cases occur in tropical areas. Indeed, nearly 50% of diarrheal disease deaths (4.6 million) occur in children under 5 years of age, living in the tropics (Snyder and Merson, 1982; Bockemiihl, 1985). Many investigators and government administrators assume that the high morbidity and mortality rates simply indicate the level of contamination of water in tropical areas. However, determining biological contamination in tropical source water is much more difficult than most reg- ulatory agencies perceive. Yet, the need to accurately determine the level of biological contamination is much greater in tropical areas than it is in temperate areas since these regions have a much greater number of waterborne diseases (Table 2.1 and 2.2). In turn, these diseases are exacerbated by the lack of adequate sewage treatment and a greater reliance on untreated (and possibly contaminated) waters as drinking water sources (Feachem, 1977; Esrey et aI., 1985). Source water quality in most tropical areas differs from that of temperate areas in three major ways: 1) physical and chemical; 2) biological; and 3) social and economic. We will examine each one of these categories, compare the standard microbial indicators in tropical source waters, and then look at tech- niques which may be more applicable to the tropics. 2.1 Physical and Chemical Characteristics of Tropical Waters The physical and chemical differences between temperate and tropical source water are perhaps the most obvious, yet are quite often the most overlooked. Water temperatures in tropical areas are higher than those in temperate areas. 32 G. A. McFeters (ed.), Drinking Water Microbiology © Springer-Verlag New York Inc. 1990