ABSTRACT
Ever since the evolution of Homo sapiens, the human population touched 1 billion by ~1800 AD. The population touched 2 billion by 1925, 3 billion by 1960, 4 billion by 1974, 5 billion by 1987, 6 billion by 1999, and 7 billion by 2011 (UN 2011). The population is projected to touch 8 billion by 2028 and 9 billion by 2054 and may stabilize at 10 billion by 2100 and beyond. Despite the exponential growth in the human population, earth’s natural resources are either ‘xed or dwindling. For example, only 2.5% of the earth’s total water reserve is fresh water (Figure 2.1). Freshwater ecosystems cover <1% of the earth’s surface (Johnson et al. 2001). There is no alternative to water, it has many competing uses, and it is a scarce commodity. As much as 40% of the world’s population and several ecosystems are already vulnerable to water scarcity (Oki and Kanae 2006), and the adverse effects of scarcity will be exacerbated by an increase in the population and its numerous demands (P‘ster et al. 2011).
