Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two types of water scarcity: physical or economic water scarcity. Physical water scarcity is where there is not enough water to meet all demands, including that needed for ecosystems to function effectively. Arid areas often suffer from physical water scarcity. On the other hand, economic water scarcity is caused by a lack of investment in infrastructure or technology to draw water from rivers, aquifers, or other water sources, or insufficient human capacity to satisfy the demand for water. Much of Sub-Saharan Africa has economic water scarcity.
Almost two thirds of the world's population — experience severe water scarcity for at least one month each year. Over two billion people live in countries where water supply is inadequate. Half of the world's population could be living in areas facing water scarcity by as early as 2025.