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]
Water footprint 
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. However, the water footprint does not provide information on how the embedded water negatively or positively affects local water resources, ecosystems and livelihoods.
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, green, and grey. 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.
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
International standard 
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.
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.
See also 
- Water resources
- Waste water
- Water crisis
- Virtual water
- Deficit irrigation
- Water resources of China
- China water crisis
- Carbon footprint
- Ecological 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.
- 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.
- 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).
- "Waterfootprint.org Water footprint and virtual water.". Retrieved 2008-05-30.
- "Waterfootprint.org Water footprint and virtual water.".
- 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