Freshwater is essential for humans and ecosystems but as shown in Fig. 1,
its distribution across the globe is uneven.
Currently, a fifth of the world’s population or around 1.2 billion people live in areas of physical water scarcity and a further 500 million people are approaching this situation (CAWMA, 2007).
In many places, water is overexploited for economic development,
especially for agricultural and industrial activities as well as for meeting the needs of the growing population (WWAP, 2009).
The pressure on the freshwater resources is expected to increase significantly with the climate change as well as with some measures for reducing the emissions of greenhouse gases, e.g.
cultivation of biofuel crops. This could cause a wide range of social
and environmental problems (Falkenmark, 2008).