Water scarcity involves the variation in water availability over space and time, mainly due to variations in seasonal and annual precipitation. It can also be a situation where water is sufficiently available but is of bad quality due to pollution, making it hazardous for human use.

The main causes include over-exploitation, excessive use, and unequal access to water among different social groups. A large and growing population leads to greater demand for domestic use and food production, resulting in the over-exploitation of water to expand irrigated areas. Additionally, pollution from domestic and industrial wastes, chemicals, pesticides, and fertilisers degrades water quality.