Water is essential for all life on Earth. While there is an abundance of water on Earth, about 97% of this is saltwater and is unsuitable for drinking. Furthermore, most of the remaining fresh water (3%) is frozen at the poles, contaminated, or otherwise undrinkable. As a result, less than 1% of all water on Earth is clean and easily utilized by humans. 
In addition to its scarcity, water also is unevenly distributed. Due to a variety of factors, primarily climate, and lack of local infrastructure, many regions suffer from seasonal or year-round water stress. According to the UN, over one quarter of the world’s population (2.1 billion people) lack access to safe drinking water. Many others must travel great distances to retrieve water from dwindling sources. 
Water stress is everywhere, not just in developing countries. California is in the midst of an major drought, and is pumping in much of its water from other states. Large-scale restrictions on water use are already being implemented. As the climate continues to undergo changes, the region may see even more extreme drought conditions in the future.