Water use can mean the amount of water used by a household or a country, or the amount used for a given task or for the production of a given quantity of some product or crop. The term "water footprint" is often used to refer to the amount of water used by an individual, community, business, or nation.
World water use has been growing rapidly in the last hundred years (see graph from New Scientist article). From 1900 to 2000, water use for agriculture went from about 500 to 2,500 cubic kilometers per year, while total use rose from around 600 to more than 3,000 cubic kilometres per year. Agriculture uses 70% of water resources.
In the U.S, the typical single family home uses about 69.3 gallons (262 litres) of water per day (2008 estimate). This includes (in decreasing order) toilet use, washing machine use, showers, baths, faucet use, and leaks.[better source needed]
The water footprint of an individual, community or business is defined as the total volume of freshwater used to produce the goods and services consumed by the individual or community or produced by the business. Water use is measured in water volume consumed (evaporated) and/or polluted per unit of time. A water footprint can be calculated for any well-defined group of consumers (e.g., an individual, family, village, city, province, state or nation) or producers (e.g., a public organization, private enterprise or economic sector). The water footprint is a geographically explicit indicator, not only showing volumes of water use and pollution, but also the locations.
The water footprint of a country is related to what its people eat. In 1993, Professor John Allan (2008 Stockholm Water Prize Laureate), strikingly demonstrated this by introducing the "virtual water" concept, which measures how water is embedded in the production and trade of food and other products. For example, it a common thought that the water involved in a cup of coffee is just the water in the cup. There is actually 140 litres of water involved. The 140 litres of water is the amount of water that was used to grow, produce, package, and ship the coffee beans. A hamburger needs an estimated 2,400 litres of water. This hidden water is technically called virtual water. Therefore, eating a lot of meat means a large water footprint. The more food comes from irrigated land, the larger is the water footprint.
The water footprint concept was introduced in 2002 by Arjen Y. Hoekstra from UNESCO-IHE as an alternative indicator of water use. The concept was refined and accounting methods were established with a series of publications from two lead authors A.K. Chapagain and A.Y. Hoekstra from the UNESCO-IHE Institute for Water Education, now at WWF-UK and University of Twente in the Netherlands respectively. The most elaborate publications on how to estimate water footprints are a 2004 report on the "Water footprint of nations" from UNESCO-IHE  and the 2008 book Globalization of Water, and the 2011 manual “The water footprint assessment manual: Setting the global standard”. Cooperation between global leading institutions in the field has led to the establishment of the Water Footprint Network in 2008 that aims to coordinate efforts to further develop and disseminate knowledge on water footprint concepts, methods and tools.
A water footprint consists of three components:
- blue water - fresh water in lakes, rivers, aquifers
- green water - water from rainwater stored in soil
- grey water - polluted water
The blue water footprint is the volume of freshwater that evaporated from the global blue water resources (surface water and ground water) to produce the goods and services consumed by the individual or community. The green water footprint is the volume of water evaporated from the global green water resources (rainwater stored in the soil as soil moisture). The grey water footprint is the volume of polluted water that associates with the production of all goods and services for the individual or community. The latter can be estimated as the volume of water that is required to dilute pollutants to such an extent that the quality of the water remains at or above agreed water quality standards.
Being sustainable means using blue water wisely and not making grey water. Humans have polluted much water. Some rivers have so much rubbish in places that boats are pushing its way through the rubbish, for example, the Lake Karachay in Russia. It was the dumping site for radioactive waste, the water under the rubbish has chemicals from factories and toilets.
An Australian water conservation specialist Bradley George Ridoutt did a study on a jar of pasta sauce and a bag of peanut M&M's. The water needed to grow tomatoes, sugar, garlic, and onions for the sauce was 197 litres. For the M&M's, cocoa and peanuts was 1,135 litres. However, tomato plants are often grown in hot, dry claimants. They get irrigation water from the same locations as human drinking water. Cocoa and peanuts in M&M's are grown where crops get rainwater from the ground. The specialist calculated that the pasta sauce was about 10 times more likely than the M&M's to ass to water scarcity. This was because the blue water used for tomatoes was much higher stress-weighted than the green water for the cocoa and peanuts. Blue water is stress-weighted because it is consumed at rates faster than its short-term replacement.
There is an elaborate Water Footprint Assessment Manual produced by the Water Footprint Network on how to calculate a water footprint
Online water footprint calculators are available:
- For most countries of the world (in English): Individual water footprint calculator
- For the USA (in English): H2O Conserve water footprint calculator
- For Finland (in Finnish): Vesijalanjälki
- For iPhone (In English): WaterAflamed iPhone water footprint calculator
In February 2011, the Water Footprint Network, in a global collaborative effort of environmental organizations, companies, research institutions and the UN, launched the Global Water Footprint Standard. ISO is working on a procedural standard on how to incorporate water footprint in a product LCA. This ISO standard will be linked to the Global Water Footprint Standard, which can be applied for different sorts of Water Footprint Assessment: for products, companies, countries or river basins.
Water footprint of products
The water footprint of a product is the total volume of freshwater used to produce the product, summed over the various steps of the production chain. The water footprint of a product refers not only to the total volume of water used; it also refers to where and when the water is used (Source: WFN Glossary). The Water Footprint Network maintains a global database on the water footprint of products: WaterStat
An individual’s daily diet of fruits, vegetables and grains requires more than 1,500 litres (396.3 US gal) of water, as compared to 3,400 litres (898.2 US gal) needed for a daily diet rich in animal protein. Research by the Cranfield University calculated the amount of water required to produce various common foods in the United Kingdom:
|Product||Amount in Litres||Amount in Gallons|
|1 cup of tea||32.4 l||8.6 US gal|
|1 imperial pint of beer||160 l||42.3 US gal|
|1 glass of wine||120 l||31.7 US gal|
|1 glass of milk||200 l||52.8 US gal|
|1 kilogram (2.2 lb) of beef||15,000 l||3,962.6 US gal|
|1 kilogram (2.2 lb) of poultry||6,000 l||1,585.0 US gal|
|250 grams (8.8 oz) packet of M&M's||1153 l||304.6 US gal|
|575 grams (20.3 oz) jar of Dolmio pasta sauce||202 l||53.4 US gal|
For more product water footprints: see the Product Gallery of the Water Footprint Network
Water footprint of individual consumers
The water footprint of an individual refers to the sum of his or her direct and indirect freshwater use. The direct water use is the water used at home, while the indirect water use relates to the total volume of freshwater that is used to produce the goods and services consumed.
The average global water footprint of an individual is 1,385 m3 per year.The average consumer in the United States has a water footprint of 2,842 m3 per year, while the average resident in China and India has a water footprint of 1,071 and 1,089 m3 per year, respectively.  The average Finnish water footprint is 1,730 m³ water per person per year, while the water footprint of the U.K. is 1,695 m³ water/person/year.
Water footprint of companies
The water footprint of a business, the 'corporate water footprint', is defined as the total volume of freshwater that is used directly or indirectly to run and support a business. It is the total volume of water use to be associated with the use of the business outputs. The water footprint of a business consists of water used for producing/manufacturing or for supporting activities and the indirect water use in the producer’s supply chain.
The Coca-Cola Company operates over a thousand manufacturing plants in about 200 countries. Making its drink uses a lot of water. Critics say its water footprint has been large. Coca-Cola has started to look at its water sustainability. It has now set out goals to reduce its water footprint such as treating the water it uses so it goes back into the environment in a clean state. Another goal is to find sustainable sources for the raw materials it uses in its drinks, such as sugarcane, oranges, and corn. By making its water footprint better, the company can reduce costs, improve the environment, and benefit the communities in which it operates. 
Water footprint of nations
The water footprint of a nation is the water used to produce the goods and services consumed by the inhabitants of the nation. The internal water footprint is the appropriation of domestic water resources; the external water footprint is the appropriation of water resources in other countries. About 65% of Japan's total water footprint comes from outside the country; about 7% of the Chinese water footprint falls outside China.
The application and interpretation of water footprints may sometimes be used to promote industrial activities that lead to facile criticism of certain products. For example, the 140 litres required for coffee production for one cup  might be of no harm to water resources if its cultivation occurs mainly in humid areas, but could be damaging in more arid regions. Other factors such as hydrology, climate, geology, topography, population and demographics should also be taken into account. Nevertheless, high water footprint calculations do suggest that environmental concern may be appropriate.
According to Dennis Wichelns of the International Water Management Institute: Although one goal of virtual water analysis is to describe opportunities for improving water security, there is almost no mention of the potential impacts of the prescriptions arising from that analysis on farm households in industrialized or developing countries. It is essential to consider more carefully the inherent flaws in the virtual water and water footprint perspectives, particularly when seeking guidance regarding policy decisions.
The use of the term "footprint" can also confuse people familiar with the notion of a carbon footprint, because the water footprint concept includes sums of water quantities without necessarily evaluating related impacts. This is in contrast to the carbon footprint, where carbon emissions are not simply summarized but normalized by CO2 emissions, which are globally identical, to account for the environmental harm. The difference is due to the somewhat more complex nature of water; while involved in the global hydrological cycle, it is expressed in conditions both local and regional through various forms like river basins, watersheds, on down to groundwater (as part of larger aquifer systems). The water footprint of a business, the'corporate water footprint', is defined as the total volume of fresh water that is used directly or indirectly to run and support a business. It is the total volume of water use to be associated with the use of the business outputs.The water footprint of a business consists of water used for producing/manufacturing or for supporting activities and the indirect water use in the producer’s supply chain. Water Credit for conserving water: Nagpur based innovator Shripad Vaidya's idea of giving water credit's, much like carbon credits, to those who save and conserve water is gaining ground. These water credits can be marketed or sold to those in need of surplus water for social,agricultural or industrial ventures.
- Water resources
- Waste water
- Water crisis
- Virtual water
- Deficit irrigation
- Water resources of China
- China water crisis
- Carbon footprint
- Ecological footprint
- Runoff footprint
- "Looming water crisis simply a management problem" by Jonathan Chenoweth, New Scientist 28 Aug., 2008, pp. 28-32.
- Nitti, Gianfranco (May 2011). "Water Is Not an Infinite Resource and the World is Thirsty". The Italian Insider (Rome). p. 8.
- "Cashing in on climate change". IBISWorld. 29 May 2008. Archived from the original on 4 October 2008.
- Definition taken from the Hoekstra, A.Y. and Chapagain, A.K. (2008) Globalization of water: Sharing the planet's freshwater resources, Blackwell Publishing, Oxford, UK.
- "Waterfootprint.org: Water footprint and virtual water". The Water Footprint Network. Retrieved 9 April 2014.
- Allan, Tony (2011). Virtual water : tackling the threat to our planet's most precious resource. London: I.B. Tauris. ISBN 978-1845119836.
- Morelli, Angela (2012). "Virtual Water - Discover how much WATER we EAT everyday". Retrieved 9 April 2014.
- Hoekstra, A.Y. (2003) (ed) Virtual water trade: Proceedings of the International Expert Meeting on Virtual Water Trade, IHE Delft, the Netherlands 
- Globalization of Water, A.Y. Hoekstra and A.K. Chapagain, Blackwell, 2008
- Hoekstra, Arjen (2011). The water footprint assessment manual: Setting the global standard. London: Earthscan. ISBN 978-1-84971-279-8.
- Naumann, Ruth (2011). Sustainability (1st ed. ed.). North Shore, N.Z.: Cengage Learning. pp. 56–58. ISBN 978-017021-034-8.
- Ridoutt, Bradley George; S. J. Eady, et al. (2009). "Product Water Footprint: How Transferable Are the Concepts From Carbon Footprinting?". Conference ALCAS(Australian Life Cycle Assessment Society). Retrieved 6 April 2014.
- Davies, Jack (31 March 2009). "Experts warn of major UK water shortage". Farmers Guardian. Retrieved 30 May 2011.
- "The Water Footprint of Humanity". JournalistsResource.org, retrieved 20 March 2012
- Hoekstra, AY (2012). "The Water Footprint of Humanity". PNAS. doi:10.1073/pnas.1109936109.
- Data obtained from the Finnish Wikipedia article page Vesijalanjälki
- Chapagain, A.K. and Orr, S. "U.K. Water Footprint: The Impact of the U.K.'s Food and Fibre Consumption on Global Water Resources, Volume 1". WWF-UK (WWF-UK). and volume 2 Chapagain, A.K. and Orr, S. "Volume 2". WWF-UK (WWF-UK).
- "2013 Water Report: The Coca-Cola Company". The Coca-Cola Company. Retrieved 8 April 2014.
- Wichelns, D. Virtual Water and Water Footprints Offer Limited Insight Regarding Important Policy Questions, Water Resources Development. Vol 26, No 4, 639–651, December 2010.
- Limca Book of Records2012 page 278