It is estimated that approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation. Some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%. Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture.

Source: Vital Water Graphics, UNEP

When demand is greater than availability or supply, it is called as scarcity. Water scarcity, as per UN norms, is defined as when water availability drops below 1,000 m3 per person. When water availability in a region drop below 1,700 m3 per person, it is called as water stress. UN rates India as water stress region. Around 700 million people in 43 countries suffer today from water scarcity. By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world’s population could be living under water stressed conditions.
Water scarcity also means that the water is available but it cannot be used for a particular activity. For e.g. water that is available, might be good for sanitation, but not for drinking purposes.