ABSTRACT
Water is both a resource for humans and an environmental habitat, which explains the many concerns we have about this ‘blue gold’. Of course, water is not as scarce as gold; on the contrary, it is a renewable resource. Water moves continually through a cycle on Earth. There are approximately 1,400 million km3
of water on Earth, but only 3 per cent is fresh water, of which 69 per cent is locked up in glaciers and snow (Oki and Kanae 2006). The remaining water is usable for humans but it is poorly distributed in the world. More than 2.5 billion people face water scarcity during at least one month of the year (Hoekstra et al. 2012), meaning that available water resources sufficient to meet demand are lacking. The future is not bright, as climate change and population growth tend to increase this threat. Human interventions and activities exacerbate the situation. This is principally owing to agriculture, which is responsible for 70 per cent of water withdrawal, whereas domestic users are responsible for 12 per cent and industrial users for 18 per cent (FAO 2012). Degradation of water quality leads to unavailable water resources for certain usage. Fresh water is also an environmental habitat that can be affected by water scarcity and pollution. In terms of biological value, rivers contain a rich and varied biota, that is, at least 100,000 species – almost 6 per cent of all described species (Dudgeon et al. 2006). Ecosystem destruction due to water abstraction, habitat alteration incurred by damming or water transfer, changes in water chemistry because of pollution, and species removal and additions are the main disturbances caused by anthropogenic activities.
