Over the past twenty years, global access to water has steadily increased.[reference: World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF). 2021.[link: https://washdata.org/reports/jmp-2021-wash-households "Progress on household drinking water, sanitation and hygiene 2000-2020: five years into the SDGs."] Geneva. Retrieved from World Development Indicators [link: https://data.worldbank.org/indicator/SH.H2O.SMDW.ZS (SH.H2O.SMDW.ZS)].] Close to three quarters of the world population used safely managed drinking water services [target: 6.1] in 2020, up from 62 percent in 2000. However this progress is threatened by increasing demand for freshwater, and the impact of climate change on the water cycle.[footnote: The continuous circulation of water between air and land by water changing states between liquid, vapor, and ice.] This chapter will focus on [target: 6.4], which seeks to ensure sustainable usage and supply of freshwater, and avert water scarcity.

Looking at the Earth, water may seem abundant. But freshwater, non-saline water that can be used for irrigation and consumed by humans, is limited.

The amount of available freshwater varies widely from country to country. Some countries are rich in surface waters, and enjoy abundant precipitation,[footnote: Water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. Source: [link: https://www.usgs.gov/special-topics/water-science-school/science/precipitation-and-water-cycle United States Geological Survey Water Science School]] while others have no surface water resources, and see little rain or snow.

Heat from the sun helps create continuous circulation from sea to air to land as water alternates its states of liquid, vapor, and ice: This is called the water cycle. Renewable freshwater resources are generated from this cycle, which is a direct consequence of countries’ geographical position. This determines the water supply, which can come from rainfall over the territory, as well as from upstream rivers or aquifers, which may be shared with neighboring countries. Thus, the renewable freshwater supply is essentially finite, even though the amount available in any given area varies from year to year due to rainfall variability.[reference: M Falkenmark, J Lundqvist, C Widstrand. 1989. [link: https://pubmed.ncbi.nlm.nih.gov/12317608/ “Macro-scale water scarcity requires micro-scale approaches. Aspects of vulnerability in semi-arid development.”] Natural Resources Forum 13(4):258-67]

Water is indispensable for humans. We need it to stay hydrated, prepare food, and maintain good hygiene. Besides such domestic use, water is an essential input to agriculture and for other goods and services. These non-domestic uses are by far the most intensive. While the UN calculates[reference: [link: https://www.un.org/en/global-issues/water United Nations Global Issues: Water]] that a person needs 50 to 100 liters of water per day to meet basic drinking, cooking, and hygiene needs, the Food and Agriculture Organization (FAO) estimates[reference: FAO (Food and Agriculture Organization). 2017. [link: https://www.fao.org/3/i7959e/i7959e.pdf “Water for Sustainable Food and Agriculture: A report produced for the G20 Presidency of Germany.“]] that “between 2,000 and 5,000 liters of water are needed to produce a person’s daily food needs”. Water is also critical for electricity production[footnote: 90 percent of global power generation is water intensive. Source: WWAP (United Nations World Water Assessment Programme). 2014. [link: https://unesdoc.unesco.org/ark:/48223/pf0000225741 The United Nations World Water Development Report 2014: Water and Energy.] Paris, UNESCO.] and sustaining biodiversity and ecosystems.[reference: [link: https://www.unwater.org/water-facts/water-and-ecosystems UN-Water: Water and Ecosystems]]

Global freshwater withdrawal is estimated to have more than doubled since 1960.[reference: UN-Water. 2021. [link: https://www.unwater.org/sites/default/files/app/uploads/2021/10/UN-Water-analytical-brief-Water-use-efficiency_October2021.pdf “UN-Water Analytical Brief on Water Use Efficiency.”]Geneva.] The large amount of water needed for food production means that water resources are predominantly allocated to the agricultural sector. Population growth is one of the primary drivers of increased water demand, as is economic growth. In addition, policy distortions and water mismanagement can contribute to water scarcity:  Water underpricing and agricultural subsidies for instance, may lead to excessive use.

In low-income countries, water use in agriculture accounts for 90 percent of all water withdrawals. This is significantly less in high-income countries (44 percent), where a higher share of water goes to the industrial sector.

Between 1960 and 2018, water withdrawals increased by 100 percent in agriculture, 90 percent in industry, and 300 percent in domestic use.[reference: UN-Water. 2021. [link: https://www.unwater.org/sites/default/files/app/uploads/2021/10/UN-Water-analytical-brief-Water-use-efficiency_October2021.pdf “UN-Water Analytical Brief on Water Use Efficiency.”] Geneva.] Although water use is becoming more efficient[reference: FAO (Food and Agriculture Organization). 2021. [link: https://www.fao.org/documents/card/en/c/cb6413en “Progress on change in water-use efficiency: Global Status and Acceleration Needs for SDG Indicator 6.4.1.”] Rome.] across all economic sectors, global demand for water is expected to keep increasing due to economic and population growth.[reference: WWAP (UNESCO World Water Assessment Programme). 2019. [link: https://unesdoc.unesco.org/ark:/48223/pf0000367306 “World Water Development Report 2019: Leaving No One Behind.”] Paris.] This growth is adding to pressure on water resources, while at the same time the water cycle is being impacted by climate change – two factors which may limit freshwater availability. It is therefore essential to monitor stress on water resources as an early warning indicator of potential scarcity.

There are different ways of defining water stress.[footnote: Please see the following [link: https://www.mdpi.com/2073-4441/13/2/201 article.]] In this story, we will use the water stress indicator defined in SDG 6.4.2.[reference: United Nations Statistics Division. SDG Indicators Metadata repository. [link: https://unstats.un.org/sdgs/metadata/files/Metadata-06-04-02.pdf “Indicator 6.4.2: Level of water stress - Definition and methodology”].] The water stress indicator seeks to estimate the amount of pressure on a country’s renewable freshwater resources.[footnote: The indicator for water stress does not consider human-made increases in water supply (such as desalination), and ignores water withdrawals that are recycled and reused.] It is defined as the ratio of total freshwater withdrawals divided by the available renewable freshwater.

The closer a country gets to 100 percent, the more pressure it places on its water resources. In some cases, the value of 100 percent can even be exceeded. This happens when a country consumes water resources that are non-renewable. This is the case for instance, when water is extracted from the non-renewable reserves of an aquifer, generally referred to as fossil groundwater.[reference: UNESCO (United Nations Educational, Scientific and Cultural Organization). 2006. [link: https://unesdoc.unesco.org/ark:/48223/pf0000146997 “Non-renewable groundwater resources.”] Paris.]In such cases, countries are over-extracting their water resources.

Countries can face water stress even if they are not over-extracting. The FAO classifies countries into five categories of water stress: None (<25 percent), Low (25-50 percent), Medium (50-75 percent), High (75-100 percent), and Critical (>100 percent).

While low water stress indicates sustainable usage, it is important to note that this is not necessarily a positive outcome: it may indicate the inability of a country to properly manage its water resources for the benefit of its population. In some low-income countries, water stress levels are very low, but access levels are also low. For example, the level of water stress in Uganda is just 5.8 percent but only 17 percent of the population have access to safely managed drinking water.[reference: World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF). 2021.[link: https://washdata.org/reports/jmp-2021-wash-households "Progress on household drinking water, sanitation and hygiene 2000-2020: five years into the SDGs."] Geneva. Retrieved from World Development Indicators [link: https://data.worldbank.org/indicator/SH.H2O.SMDW.ZS (SH.H2O.SMDW.ZS)].] The water stress indicator signals the importance of effective supply and demand management policies.[reference: FAO (Food and Agriculture Organization) and UN-Water. 2021. [link: https://doi.org/10.4060/cb6241en “Progress on the level of water stress: Global status and acceleration needs for SDG indicator 6.4.2, 2021.”] Rome.]

The Nile basin is a striking example of transboundary water resources, but it is not isolated: At least 310 of the world’s river basins are shared by at least two countries, and the majority of global freshwater flows (60 percent) comes from these basins.[reference: Carius, Alexander, Geoffrey d. Dabelko, and Aaron T. Wolf. 2004. [link: https://www.wilsoncenter.org/sites/default/files/media/documents/publication/ecspr10_unf-caribelko.pdf “Water, Conflict, and Cooperation”.] Environmental Change and Security Program Report Issue 10, 60-66. Wolf, Aaron T., Annika Kramer, Alexander Carius, and Geoffrey D. Dabelko. 2005. [link: https://transboundarywaters.science.oregonstate.edu/sites/transboundarywaters.science.oregonstate.edu/files/Publications/Wolf%20-%20SOW%2005%20chap5.pdf “Managing Water Conflict and Cooperation”]. In State of the world 2005: A Worldwatch Institute Report on progress toward a sustainable society: global security. 80-99.]

In many regions, economic development and population growth have put pressure on freshwater resources. Climate change represents an additional challenge as it is already impacting, and will likely continue to affect the quality and quantity of water in many river basins.[reference: Caretta, M.A., et.al., 2022. [link: https://www.ipcc.ch/report/ar6/wg2/ Water. In: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change].] Climate change intensifies the water cycle, increasing evaporation and precipitation. Regions with high rainfall will see more rainfall during shorter periods of time (increased risk of flooding), while arid and semi-arid regions will receive less rain over longer periods of time, creating an increased drought risk.[reference: OECD (Organisation for Economic Co-operation and Development). 2013. [link: https://doi.org/10.1787/9789264200449-en “Water and Climate Change Adaptation: Policies to Navigate Uncharted Waters”, OECD Studies on Water, OECD Publishing.]] This situation calls for extended institutional collaboration, and is forcing governing bodies to rethink their water management practices. This is happening in the Colorado River Basin.

The United States, as a country, has a low water stress level (28 percent), but there are large regional differences. [link: https://www.usbr.gov/uc/img/crsp/CRBMap.jpg The Colorado River Basin], located in the Southwest, has a high level of water stress (79 percent). The Colorado River is about 1,450 miles long (2,334 km) and the basin area includes seven states (Wyoming, Utah, Colorado, New Mexico, Arizona, Nevada, California), and parts of northern Mexico. The river is an important water source: It irrigates nearly 4.5 million acres (18,210 km²) of agricultural lands, generates more than 4,200 megawatts of electrical capacity per year, and provides water to around 40 million people.[reference: Bureau of Reclamation, U.S. Department of Interior. 2021. [link: https://www.usbr.gov/climate/secure/docs/2021secure/basinreports/ColoradoBasin.pdf Colorado River Basin—SECURE Water Act Section 9503(c)—Report to Congress. ]] The majority of this region has an arid or semi-arid climate.[footnote: Defined by precipitation per year: 0-250 mm for arid climate and 250-500 mm for semi-arid climate.] In addition, the basin has had a severe drought since 2000. According to the United States Bureau of Reclamation, the period from 2000 through 2018 was the driest 19-year period in over 100 years of record keeping.[reference: United States Bureau of Reclamation. 2019. [link: https://www.usbr.gov/lc/region/g4000/aop/AOP19.pdf “Annual Operating Plan for Colorado River reservoirs, 2019”].] For the first time ever, the federal government officially declared a water shortage in the Colorado River in 2021. Lake Mead, the largest reservoir in the U.S. in terms of water capacity, is used to illustrate the declining water levels in the Colorado River Basin.

Lake Mead is the largest reservoir in the United States by volume, and was formed in 1936 following the construction of the Hoover Dam. Its water level has declined since 2000.

Each year, 16.5 million acre-feet (MAF) (20.3 km³) per year of water [footnote: Roughly equivalent to 8 million Olympic-sized swimming pools. Source: [link: https://regioncwater.org/glossary/acre-foot/ The Region C Water Planning Group]] from the Colorado River is shared across seven U.S. states and Mexico. This is based on [link: https://www.usbr.gov/lc/region/pao/pdfiles/crcompct.pdf the 1922 Colorado River Compact], the foundational document governing the basin’s water management. When the Compact was created, the Colorado River’s annual flow was estimated at around 18 MAF (22.3 km³) per year.[reference: Koebele, Elizabeth and Max Robinson. 2021. [link: https://www.unr.edu/nevada-today/blogs/2021/impact-of-colorado-river-shortages-on-nevada “The impact of Colorado River water shortages on Nevada: Changes to water policy needed as time runs out.”] Nevada Today, November 12, 2021]

Between 2000-2020, the annual flow declined to 12.5 MAF (15.4 km³) per year,[reference: Bureau of Reclamation. [link: https://www.usbr.gov/lc/region/g4000/NaturalFlow/current.html Colorado River Basin Natural Flow and Salt Data.]] but a total of 16.5 MAF (20.3 km³) per year of water is still being allocated to the U.S. states and Mexico.

To prevent further depletion of water resources, the federal government set the guidelines[reference: Bureau of Reclamation. [link: https://www.usbr.gov/ColoradoRiverBasin/#InterimGuidelines Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead].] governing Colorado River operations.

Around 30 percent of water has been cut for central Arizona agricultural usage.[reference: [link: https://azwaternews.com/2021/08/16/arizona-heads-into-tier-1-colorado-river-shortage-for-2022/ Arizona Municipal Water Users Association]] Water supplies to cities and industries are not changed, but Scottsdale, Arizona, is asking all residents, businesses, and visitors to conserve water usage by at least 5 percent.[reference: [link: https://www.scottsdaleaz.gov/water/news/Scottsdale-asks-residents-to-use-five-percent-less-water-and-conserve-more City of Scottsdale Water News], January 11, 2022.] The federal government warns that the level of Lake Mead will continue to decline and has called for further Basin-wide conservation efforts.

Water is a precious resource. Amid pressures from human activities, and uncertainties linked to climate change, robust water management will be critical to the sustainable use of freshwater resources. This is especially important when considering the interdependencies that exist between water, food production, energy, ecosystems, and economic activities.

Robust water management systems cannot exist without accurate and timely monitoring. However, numerous data gaps exist. As the main source of freshwater, aquifers face situations of depletion and pollution in various regions of the world, but there is little available data about the quality and quantity of groundwater.[reference: Ravenscroft, Peter, and Lucy Lytton. 2022. [link: https://openknowledge.worldbank.org/handle/10986/37197 Seeing the Invisible : A Strategic Report on Groundwater Quality.] Washington, DC: World Bank.] Water stress information is also far from complete.[reference: FAO (Food and Agriculture Organization) and UN-Water. 2021. [link: https://www.unwater.org/sites/default/files/app/uploads/2021/08/SDG6_Indicator_Report_642_Progress-on-Level-of-Water-Stress_2021_ENGLISH_pages-1.pdf Progress on Level of Water Stress. Global status and acceleration needs for SDG Indicator 6.4.2, 2021.]]

Various initiatives are being undertaken to address this situation. The World Bank is contributing to this effort through the [link: https://www.ciwaprogram.org/data-initiatives Cooperation in International Waters in Africa], the [link: https://wbwaterdata.org/ibnet International Benchmarking Network for Water and Sanitation Utilities], and the [link: https://wbwaterdata.org/siasar Rural Water and Sanitation Information System]. The upcoming World Bank report “The Hidden Wealth of Nations : The Economics of Groundwater in Times of Climate Change” will also seek to provide additional data and a “comprehensive understanding of the importance and value of groundwater for development under evolving conditions”.