Water, the liquid of life, like air and soil, has no substitute. Life as we know it would not exist without water. The geosphere, atmosphere and biosphere are all linked to and through water. Water interacts with solar energy to determine climate and transforms and transports the physical and chemical substances necessary for all life on earth. While 70% of the planet's surface is covered in water, most of it is salt water; Fresh water is limited and is not always in the right place, at the right time or of the right quality. Water on Earth exists in several states: water vapor and clouds in the sky, seawater in the oceans, icebergs in the polar oceans, glaciers in the mountains, freshwater lakes, rivers and fresh and salt water in aquifers. There are significant differences between continents and countries in the availability of fresh water. Over the past 25 years, these differences and the importance of water have become a major concern on national and international agendas. Many international organizations, such as the United Nations, the World Bank, the World Health Organization, the World Meteorological Association, and the Stockholm International Water Institute, organize conferences on water-related issues. water. Awareness among scientists, political leaders and citizens of the links between climate change, the hydrological cycle, food production, environmental services, infrastructure needs and sustainable management of water resources is increasing every year. The message highlighted by all of these efforts is that water is an increasingly scarce resource and that it is important to recognize and accept that water supplies are limited. Competition between agriculture, industry and cities for limited water supplies is already limited...... middle of paper ......). Although floods and droughts have always plagued humanity and agriculture, they serve to increase awareness of water issues and the need to use and manage water resources wisely. As a prelude to sustainable water management for agriculture and food systems, this chapter briefly describes water supply and use drivers and challenges for the future. It begins by briefly providing an overview of the physical and chemical uniqueness of water before discussing the location, availability, and uses of water. A section on “virtual water” provides information on the amount of water incorporated into foods, fibers and products. The impacts of drought and climate change on water availability are described. Before the conclusion, issues related to the sharing and management of transboundary surface and groundwater resources are highlighted. These questions will become increasingly complex as the climate changes.