Water (H2O) is one of the most common molecules on earth and a critical one for the existence of life. As such, there are countless uses for water. Not only does water sustain life through several uses, but it is a critical component in manufacturing, transport and energy. Water also is a key component in many recreational activities. Water is one of the most used compounds on earth.

The most common use of water is through drinking. People drink water almost every day and would not be able to survive without doing so. Water is also used in everyday life for cooking, cleaning, washing and playing. These activities use on average 90 gallons of water per day for the average American. Except when asleep, it is rare to go more than a couple of hours without some interaction with water.

Agricultural use of water is one of the most common uses of water. Not only are crops watered through various applications of water, but livestock also require daily use of water. Techniques such as irrigation, spraying, flooding and relying on natural precipitation all aid agriculture. Water is provided from reservoirs, canals and wells as key sources for agriculture. Fisheries and open water harvesting of seafood is a further example of how water is a part of agriculture.

Many often initially think of hydroelectric power generation when considering the use of water in energy generation. However, the use of water goes far beyond that. Water wheels are still used around the world to produce mechanical energy. Water is also a critical function in the production of energy in fossil fuel-based generation plants. The fossil fuels are burned in order to convert water into steam, which in turn is used to turn the turbines that generate the electricity.

Water plays a critical role in numerous industries. It is the most common cooling agent for many heat-intensive industrial applications. It is a common solvent in many chemical processes and is also a common component in washing and cleaning steps in many processes. Water also is used in transportation on several scales in industry. Not only are goods transported by ships and barges, but raw materials are often transported by slurry in many industries, most especially mining. There are very few heavy industries that do not use water in part of their process.