The science of water - An introduction to its amazing properties (2025)

by Chris Woodford. Last updated: June 23, 2022.

Pour yourself a glass of water and youcould be drinking some of the same molecules that passed through the lips of Julius Caesar, Joan ofArc, Martin Luther King, or Adolf Hitler. Indeed, since the human bodyis about 60 percent water you might even be drinking a tiny part of oneof those people! Water is one of the most amazing things aboutEarth; without it, there would be no life and our planet would be acompletely different place. One of the truly amazing things aboutwater is that it's never used up: it's just recycled over and overagain, constantly moving between the plants, animals, rivers, and season Earth's surface and the atmosphere up above. Let's take a look atthis life-giving liquid and find out what makes it so special!

Photo: Water covers over two thirds of Earth's surface and is an essential ingredient for all the flourishing life our planet enjoys—including this lily of the valley plant.

What is water?

We can answer that question in many different ways. Water is whatwets windows when it rains, what we drink when we feel thirsty, andwhat covers about 70% of Earth's surface. But what exactly is it?

Chemically speaking, water is a liquid substance made ofmolecules—a single, large drop of waterweighing 0.1g contains about 3 billion trillion (3,000,000,000,000,000,000,000) of them! Each molecule ofwater is made up of three atoms: two hydrogenatoms locked in a sort of triangle with one oxygen atom—giving us thefamous chemical formula H2O. The slightlyimbalanced structure of watermolecules (explained in the box below) means they attract and stick to many different substances.That's also why all kinds of things will dissolve in water, which issometimes called a "universal solvent". Water can even dissolvethe solid rocks from which our planet is made, though the process doestake many years, decades, or even centuries.

Most of the water in our world is a combination of "ordinary"hydrogen atoms with "ordinary" oxygen atoms, but there are actuallythree different istopes (atomic varieties)of hydrogen and eachof those can combine with oxygen to give a different kind of water. Ifdeuterium (hydrogen whose atoms contain one neutron and one protoninstead of just one proton by itself) combines with oxygen, we getsomething called heavy water, which is about10% heavier thannormal water. Similarly, tritium (hydrogen with two neutrons and oneproton) can combine with oxygen to make something called superheavywater.

Water has no end of amazing properties. It comes in three wildlydifferent kinds, it's heavy, it expands in a funny way, it can climb upwalls, and... oh let's find out more!

Water, ice, and steam

One of the unique things about water in the world around us is thatit exists in three very different forms (or states of matteras they are known): solid, liquid, and gas. Ordinary, liquid water is the most familiar tous because water is a liquid under everyday conditions, but we're alsovery familiar with solid water (ice) and gaseous water (steam and watervapor) as well.

Photo: Three states of water: 1) Solid snow and ice in winter;2) Liquid water splashing over the weir of a river; 3) Steam (water vapor) condensing as itemerges from the chimney of a steam engine.

Converting water between these three different states is remarkablyeasy. All you have to do is change its temperature or pressure. Takesome ice and heat it up and you'll soon have a pool of liquid water.Carry on heating it and the water will evaporateand becomesteam. It takes a terrific amount of energy to turn ice into water andwater into steam because you have to physically rearrange the structureof the substance in each case and push the molecules further apart.That's why kettles take so long to boil. (There's an easier way to turnwater from a solid or liquid into a gas and that's simply to leave itout in the open air; gradually, the more energetic molecules in thewater will escape and turn into a cool vapor up above it.)

When you heat water to make steam, there comes a point where youkeep heating the water but the temperature doesn't increase. The energyyou supply seems to be vanishing into thin air, but it's actuallypushing apart the molecules in liquid water and turning them into agas. In the process, that energy is becoming locked inside the steam assomething called latent heat (the wordlatent just means"hidden"). Latent heat is like an immense reserve of energy locked insteam that theinventors of yesteryear used to power factory machines and vehiclesusing their mighty steam engines.Read more in our main article on heat.

Photo: Steam geysers are produced when water isheated by Earth's internal heat (geothermal energy).Picture by Carol M. Highsmith, courtesy of Gates Frontiers Fund Wyoming Collection within the Carol M. Highsmith Archive, Library of Congress, Prints and Photographs Division..

Why does water make pressure?

If you've ever found yourself washing a car with buckets or wateringa garden with cans, you'll have noticed just how heavy water can be.That's because it's a relatively densesubstance (it packsan awful lot of mass into a relatively small space). Water isn'tdense compared to metals such as gold, which is almost 20 times heavierby volume. But it's much heavier and denser than wood and plastic, whichis why those things will float. Anything less dense than water floatson it; anything more dense sinks in it.

The weight of water is what causes pressurein the oceans toincrease with depth. The deeper you go, the more water there is upabove you pressing down—and that makes things particularly challengingfor submarine designers and scuba divers. Water pressure increases indirect proportion to your depth, so if you go down 100 meters thepressure is ten times greater than if you go down 10 meters. Justimagine walking on the seabed with lots of buckets of water pressingdown on your head. At a depth of about 10 km (6 miles) under theoceans, the pressure is as great as the weight of a fully-loadedarticulated lorry pressing down on anarea the size of your two feet!

Why does water expand when it freezes?

Everyone knows things get bigger when they get hotter and shrinkwhen they cool. Thermometers tell the temperature that way because the(liquid) mercury metal inside them expands as it heats up and contractswhen it cools down. But water is different. Almost uniquely, waterexpands as it starts to freeze! This amazing trick is called the anomalousexpansion of water—and here's how it works.

If you start off with a glass of water and cool it down, themolecules start to move closer and lock together. But at a temperatureof about 4°C (39°F), the molecules are as close as they canpossibly get. In other words, the water has reached its maximumdensity. If you keep on cooling it down, the molecules rearrangethemselves into a slightly more open structure. This means ice is alittle bit less dense than freezing water and that's why ice floats onwater that's the same temperature.That's extremely important for fish and all kinds of other river andsea creatures, because it means they can survive in winter in theliquid water underneath solid frozen ice.

Artwork: The "anomalous expansion of water": Left: In liquid water, molecules are held loosely but closely by weak and random hydrogen bonds that are constantly breaking and reforming.Right: In solid water (ice), molecules are held by stronger bonds in a more open but rigid structure. Thereare fewer molecules in a given volume, which is why ice is less dense than—and floats on—water.

Unfortunately, people don't always find the anomalous expansion ofwater so helpful. If the water pipes running under your home freezesolid in winter, the water inside them will turn to ice that takes upmore volume—causing the pipes to burst open and then leak when the icethaws out. Why don't we simply use stronger pipes? It wouldn't makemuch difference: water expands with incredible force when it freezesand even very thick metal pipes would still burst. You can watch asuperb video demonstration of a bursting pipe from Steve Spangler.

Photo: Ice is a life raft for polar bears, which use floating ice to help them feed on sea creatures such as seals. Picture by Erich Regehr courtesy of US Fish & Wildlife Service.

Why does water take so long to heat up?

Has that kettle boiled yet? Well tell it to hurry up—I'm dying for acup of tea! It may be a nuisance if you're cooking or making drinks,but the length of time it takes water to absorb heat is very useful tous in other ways. Water has a high specific heatcapacity and that means it can hold or carry more heat per kilogram (or pound) thanvirtually any other substance. That's why we use water in heatingsystems such as radiators, because each liter of water that tricklesthrough the pipes carries and delivers more heat. Of course thedrawback is that the water takes some time to heat up in the firstplace—but on the other hand, the water in your bathtub willstay hotter, longer for exactly the same reason.

If you like swimming outdoors, high specific heat capacity explains why,in some parts of the world, seas, lakes, and rivers aren't as warm as youthink in the early summer: huge volumes of water take a long time to heat upafter a cold winter and spring. By the same token, the water will still be warm enough for swimming in chilly parts of Europe well into the fall (autumn) when the air temperature has already started to plunge.

Why can insects walk on water?

Artwork: Water striders and similar insects float using long, water-repellent (hydrophobic) legs to spread their weight over a large surface area.

You've probably seen insects that can walk on water. They'resupported by a kind of invisible "structure" on the surface known as surfacetension. It happens because water molecules attract verystronglyto one another—that's also why water forms droplets on windows ratherthanspreading out in a perfectly thin film, as oil would. Imagine all thedrops in a basin full of water trying to attract one another.Effectively, they're "linking arms" and forming an invisible skin onthe surface that's strong enough to support things like needles andrazor blades that are heavy enough to sink. All kinds of insects,including spiders, pondskaters,and water boatmen, use surface tension to move across water. In theory, you could walk onwater too if you could spread your weight across a big enough area totake advantage of surface tension.

How does water climb up a tube?

Artwork: Water (left) climbs up the sides of a tube to form a downward-curving surfacecalled a concave meniscus. Liquid mercury (right) does the opposite, forming an upward-curving (outward-bulging) convex meniscus.

Put some water in a glass and you'll see that it doesn't form aperfectly straight surface: it actually climbs up the glass slightlymore at the edges, forming a downward curving surface called a concave meniscus.The thinner you make the glass (that is, the smaller the diameter itis), the more the water will climb. Put water in a narrow glass rod andyou can make it climb up quite a distance. This is known as capillaryaction or capillarity. It's how bloodmoves through ourveins and how water is sucked up through the stems of plants and trees.Capillarity helps a large oak tree to suck up something like 380 liters(100 gallons) of water each day!

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Water in our world

Photo: Earth's atmosphere is full of water vapor. Computer-processed satellite photograph courtesy of NASA on the Commons.

So much of Earth is covered in water that the planet couldeasily be called Aqua or Oceanus. Apart from the water on the surface(in oceans, rivers, lakes, and creeks), there's also a vast amount ofwater swirling around in the atmosphere (in clouds, mist, and fog) andplenty more trapped in rocky underground reservoirs called aquifers.Earth's water—perhaps its most unique feature—was formed after the BigBang (the explosion that created the Universe about 13.7 billion yearsago). About 4.6 billion years ago, when our solar system was created, amixture of hydrogen and oxygen atoms joined together to make clouds ofhot steam that eventually cooled to form water, which fell to Earth asrain, formed the oceans and carved the continents into shape.

Water for life

Life began on Earth about a billion years later (3.6 billion yearsago), initially in the oceans. Although many species now live on land,they still need water to live and grow: humans, for example, could gowithout food for about two months, but we'd die of thirst if we wentmore than a week or so without a drink. Typically we need at least 2liters of water a day to survive, though we get much of this fromthings we eat as well as things we drink. Eggs are about three quarterswater, for example, while fruits such as oranges and melons are over 90percent water.

We drink only about 1 percent of the water we consume each day anduse the other 99 percent (about 250 liters a day) to feed things likebaths, showers, washing machines,lawn and garden sprinklers, hosepipes for washing cars, and flushtoilets. Aclothes washing machine can easily use over 100 liters in an hour byrepeatedly rinsing your laundry to remove detergent. Lots of productswe'd never normally associate with water consume vast amounts of theprecious liquid during their manufacture. About 570 liters of water isused making a thick Sunday newspaper, for example.

To people in developing countries, many of whom lack access torunning water, all of this would seem amazingly wasteful. As Earth'spopulation grows and each person needs more and more water, thepressure on our planet's water resources will grow too. Theoretically,on a planet covered with water, supplies should never run out—but mostof Earth's water is salty and undrinkable. Turning it into usablefreshwater means using costly, energy-hungry desalination plants. Thegrowing pressure on water has led some politicians to speculate thatwars may be fought over scarce water supplies before the end of the21st century.

Chart: Four key world water statistics. Overall, 17 percent of the world's water is classed as "stressed" (North Africa and the Middle East are most stressed, and Canada and Icelandare among the least stressed)); 60 percent of the world's people have access to basic handwashing; 45 percent have basic sanitation; and 71 percent have safe drinking water.Source: 2017 data retrieved in 2020 from UN Water SDG6, 2020.

The water cycle

There's a lot of talk about recyclingto help the environment but water is one thing we recycle without eventhinking about it. Every time we flush a toilet or empty a washing-upbowl down the drain, the water we've used disappears down waste pipes,passes through the sewerage and wastewater system, and reappears(hopefully) as good as new in our rivers and seas. Admittedly, water pollution is still a very seriousproblem, but one thing we can count on is that water will constantlycirculate between Earth's surface and the atmosphere up above in thenever-ending water cycle. Water's been circulating round our planet forbillions of years—and it's not about to stop anytime soon!

Artwork: The Water Cycle illustrated by John M Evans for the US Geological Survey. You can find a bigger version of this picture on the USGS Water Cycle page.

Saving water

Next time you're flushing your toilet, washing your car, firingthe sprinkler over your garden or cleaning your windows, spare athought for the 2 billion people (26 percent of the world'spopulation) who still have no safe supply of clean waterand the 3.57 billion people (46 percent of the population) who don't have propersanitation [Source: World Health Organization: Sanitation and World Health Organization: Drinking Water, 2022]. Imagine how people in some remote village in Africa would feel if they could see you squandering gallons of sparkling, clean,highly treated water that you're not even going to drink.

Chart: Right: How we use (and waste) water in our homes. If you had to walk foran hour to fetch your water, would you let so much run down the drain? Drawn using data compiled by American Water Works Association/Water Research Foundation.

On one level, this is an utterly ludicrous comparison: even if you savewater, it doesn't help people in Africa one iota.But on another level, conserving water is incredibly important: asglobal warming and climate change kick in, virtually all of us will find our waterresources under much greater pressure. Saving water obviously saveswater, but it also saves energy(because cleaning water is very energy intensive), protects rivers(because water ultimately comes from there), and helps the environment on which we all depend. Ifyou're billed for every unit of water you use, saving water alsohelps your pocket. That's why many people are interested ingreywater: a way of collecting and recycling some of yourhousehold water and using it for less important things likeflushing the toilet.

What is greywater?

According to the US Environmental Protection Agency (EPA), a typical family can use an astonishing 1100 liters (300 gallons) of water a day in total.Even allowing for cooking and hand-washing, where we need to use clean water,there's a huge mismatch between how much water we use in total and the amount we need that has to be scrupulouslyclean. Greywater systems try to address this.

Photo: A simplified diagram showing the basic idea of greywater: some household water is relatively clean even after it's used, so it makes sense to use it for less important jobs. In the configuration shown here,a white water tank in the roof supplies the washbasin, bath-tub, and washing machine (blue lines). They drain (black lines) into a greywater tank (center), which is used to flush the toilet (red line). Spent water from the kitchen sinkand toilet go straight to the sewer as black water.

Greywater (sometimes spelled graywater in the UnitedStates) is the idea of having two separate household water systems.First, you have a normal household water supply of clean, fresh water(sometimes called whitewater or mains water), which you usefor drinking, cooking, and so on. But you also have an extra tankthat collects the used water from your bath tub, shower,clothes washing machine,(and sometimes your outside roof). This is your greywater. It's usedfor flushing the toilet (automatically), but you can also use it forwashing the car, watering the garden, and anything else that doesn'tneed absolutely clean water. Sometimes water from the kitchen sink(dark greywater) is reused too, but it's more contaminated andunhygienic than water from your bath or shower. Water from the toilet(known as blackwater) is never reused: it's discharged to thesewer in the usual way. Trials by the UK'sEnvironment Agency (a similar organization to the US EPA) have found that systems like thiscan save 5–36 percent of total household water consumption, thoughmuch less (a maximum of about 20 percent) in efficient new homes.

Advantages and disadvantages of greywater systems

Photo: Greywater typically means installing an extra tank. This large tank is being put into a school; you wouldn't need a tank quite so big for a home. Photo by Felix Garza Jr. courtesy ofUS Navy.

Greywater sounds like a brilliant idea—for all sorts of reasons.First, it reduces the fresh water you need to consume, so it could helpto cut your water bill. If you're consuming less water, the sewage andwastewater plants have to recycle less (using less energy) and less water has to beremoved ("abstracted") from rivers—so greywater is also good for the environment.If you have a septic tank, switching to greywater reduces the amount of water you're passingthrough the tank for treatment, extending its life.

But there are disadvantages too. First, the cost of installing agreywater system can be significant compared to the savings in waterbills you actually make. More seriously, storing used water asgreywater allows microorganisms to breed—especially if it's warmwater to begin with—and that can present a health hazard. Sograywater has to be stored carefully with hygiene in mind, typicallyeither filtered before being stored, chemically disinfected, orstored for only relatively short periods of time (greywater systemsautomatically flush their tanks and refill with clean white water ifthey're unused for too long) to reduce the chanceof bacterial contamination.

Alternatives to greywater

Photo: This low-maintenance garden at DOE/NREL in Golden, Colorado is a good example of how office gardenscan be redesigned to save the need for wasteful irrigation. Photo by Warren Gretz courtesy ofUS DOE/NREL (Department of Energy/National Renewable Energy Laboratory).

Purification, disinfection, and periodic draining clearlyreduces the benefit of having a second water system—so much so that,for small households, there may be no benefit at all. You canprobably achieve greater savings more quickly and economically simplyby using fresh water more carefully: by flushing yourtoilet less often (or converting to a water-saving dual-flush),turning off the faucet (tap) while you brush your teeth, installing a low-flowshower nozzle (one that mixes a lot of air with the water), using a water butt to collect rainfall for your garden, and so on. Water savings like this are really easy to make;many are instant and free. One really good way to save water is toask your utility company to install a water meter on your property(if you don't have one already). Seeing how much water you use eachmonth or quarter (and how much it costs, on your bill) really focusesthe mind on making savings—and you can see just how effectiveyou're being.

Environmentalists tend to see things a little bitdifferently. The very concept of wasting a resource as precious aswater is galling to people who truly value the planet, so somegreen-minded people insist on installing greywater systems ineco-homes as a matter of principle. Environmentalists or not, themessage is clear: in a world of growing water scarcity, all of ushave a responsibility to use this important resource more carefully.It's worth bearing mind that in the future, saving water may not be amatter of choice.

Find out more

Books and reports

• Greywater, Green Landscape: How to Install Simple Water-Saving Irrigation Systems in Your Yard by Laura Allen. Storey, 2017. From the basic concept of greenwater to the practicalities of planning codes, this book offers a complete guide to home water saving and recycling.
• The New Create an Oasis with Greywater by Art Ludwig. Oasis, 2016. A practical guide to building and using your own greywater system. Written for US readers, so bear in mind planning laws and restrictions may be different if you live elsewhere.
• Introduction to Greywater Management by Peter Ridderstolpe. EcoSansRes/Stockholm Environment Institute, 2004. A useful 20-page introductory report describing greywater systems, problems of pollution and management, and how to plan the right sort of system in different situations.
• Reusing and harvesting water: Useful guidance from the UK Environment Agency, including a link to their Greywater Information Guide.

Patents

• Water recirculation system by Ed Toms, Water-Cyk Corporation. Issued September 26, 1978. An early greywater system from the 1970s.
• Water recirculation system with solids and foam removal by Ed Toms, Water-Cyk Corporation. Issued April 15, 1980. A modified version of the system above, with extra features designed to reduce odors.

A brief history of water

• 4.6 billion years ago: Earth's water supplies are formed.
• 3.6 billion years ago: Water allows life to begin on Earth.
• Prehistoric times: People live nomadically, constantly movingbetween places where water and food are plentiful. The first permanentsettlements grow up next to rivers and water systems that can ensurea steady supply of water.
• ~4000BCE: Irrigation (technology for carrying a steady supply ofwater to growing crops) is invented in Mesopotamia.
• Ancient Greek philosopher Thales of Miletus(c.624BCE–546BCE) considers water the most basic building block ofmatter. Aristotle, another Greek philosopher, sees water as one of the four fundamental elements (Earth,air, fire, water).
• ~300BCE: Ancient Romans pioneer aqueducts for supplying water to their empire.
• 1582: First modern waterworks are constructed in London, England.
• 1652: First waterworks are constructed in North America in Boston, Mass.
• 1781: English scientist Henry Cavendish(1731–1810) makes water from "inflammable air" hydrogen and "dephlogistated air" (oxygen air).
• 1783: French chemist Antoine Lavoisier (1743–1794) shows that water is a compound made of hydrogen and oxygen.
• 1804: Frenchman Joseph Louis Gay-Lussac (1778–1850) and German Alexander von Humboldt (1769-1859) show that hydrogen combines with oxygen in the ratio two to one, as in the modern formula H2O.
• 1932: US chemist Harold Urey (1893–1981) discovers deuterium and shows it is present in ordinary water in tiny amounts.
• 1957: The world's first desalination plant (making freshwater by removing salt from seawater) begins operating in Kuwait.
• 1951: American chemist Aristid V. Grosse (1905–1985) discovers tritium in ordinary water.
• 2008: NASA discovers water on Mars.

Find out more

On this website

• Climate change and global warming
• Environmentalism
• Organic food and farming
• Water pollution

Facts and statistics

• Water Use and Stress by Hannah Ritchie and Max Roser, Our World in Data, 2015/2018. A graphical guide to the world's water problems.
• UN Water: A great overview of world water issues and what's being done about them.
• World Health Organization: Water: A health perspective on clean water and sanitation.
• UN Water Facts: Definitive worldwide statistics about human water consumption.
• UN Water SDG6: A database of current water and sanitation statistics.
• Key water aid statistics: How many people lack access to water? How many children die from water-related illnesses and diseases? These and more quick facts from WaterAid.
• United Nations Environment Programme: Global Environmental Outlook 6: If you're looking for more detailed water statistics, this is the place to go: UNEP's regular GEO reports contain up-to-date assessments of freshwater resources for all regions of the world.

Issues

• World water crisis: A clickable BBC introduction compares water shortages around the world. A little out-of-date, but still a decent introduction to the issues.
• The World's Water: An excellent resource from Peter Gleick (currently at Volume 9, released January 2018),including the Water Conflict Chronology, a historical tour of water warsand other conflicts.
• Water: The Big Issue for the 21st Century A talk by leading British environmentalist Sir Crispin Tickell. [Archived via the Wayback Machine.]
• The New Water Politics of the Middle East by Ilan Berman and Paul Michael Wihbey. Strategic Review, Summer 1999.

International organizations concerned with global water policy

• European Union - Water quality in the EU
• International Water Management Institute (IWMI)
• IRC International Water and Sanitation Centre
• The Nile Basin Initiative: A long-term effort to promote peaceful water-sharing among the countries dependent on the River Nile.
• Pacific Institute for Studies in Development, Environment, and Security
• Stockholm Water Institute: home of the prestigious Stockholm Water Prize
• World Bank: Water and sanitation
• World Health Organization: water, sanitation, and health
• World Water Council
• World Water Day: Join the movement for action around the World Water Day, 22 March of each year.

International agreements

• The Dublin Statement on Water and Sustainable Development. Adopted bythe International Conference on Water and the Environment (ICWE) in Dublin, Ireland, on 26-31 January 1992.
• Chapter 18: Protection Of The Quality And Supply Of Freshwater Resources: Application Of Integrated Approaches To The Development, Management And Use OfWater Resources. from Agenda 21 of the United Nations, as adopted by the Plenary in Rio de Janeiro, on June 14, 1992:

Useful reports and data on the state of world water

• World Water Council Reports: Many useful reports and documents.
• International Rivers. Various reports on dams and related river-development issues.
• UN Water Scarcity.
• [PDF] World Water Demand and Supply, 1990 to 2025: Scenarios and issues byDavid Seckler, Upali Amarasinghe, David Molden, Radhika de Silva, andRandolph Barker. Colombo, Sri Lanka: International Water Management Institute,1998.
• Appraisal and Assessment of World Water Resources byIgor Shiklomanov, Water International, Volume 25, Number 1, March 2000.
• Tearfund. Running on Empty: A Call for Action to Combat the Crisis of Global Water Shortages. London: Tearfund, 2001.
• [PDF] WaterAid. Mega-Slums: The Coming Sanitary Crisis. London: WaterAid.

Books and journal articles

• Gleick, Peter. The World's Water: The Biennial Report on Freshwater Resources: Volume 9. Washington DC: Island Press, 2018.
• Cosgrave, William et al. World Water Vision: Making Water Everybody's Business London: Routledge, 2014.
• Barlow, Maude. Blue Covenant: The Global Water Crisis and the Coming Battle for the Right to Water New York: The New Press, 2013.
• Postel, Sandra. The Last Oasis: Facing Water Scarcity London: Earthscan, 2013 (originally published in 1992).
• Pearce, Fred. When the Rivers Run Dry: Water—The Defining Crisis of the Twenty-first Century. Boston: Beacon Press, 2007.
• De Villiers, Marq. Water: Water: The Fate of OurMost Precious Resource. New York: Mariner Books, 2001.
• De Villiers, Marq. Water Wars: Is the World'sWater Running Out? London: Weidenfeld, 1999.
• Postel, Sandra. Pillar of Sand: Can the Irrigation Miracle Last? New York: W.W. Norton, 1999.
• Seckler, David, Upali Amarasinghe, David Molden, Radhika de Silva, and Randolph Barker. World Water Demand and Supply, 1990 to 2025: Scenarios and issues. Colombo, Sri Lanka: International Water Management Institute, 1998.
• McCully, Patrick. Silenced Rivers. London: Zed Books, 1996.
• [PDF] Postel, Sandra, Gretchen Daily, and Paul Ehrlich. "Human Appropriation of Renewable Fresh Water." Science, February 1996, Vol 271, p. 785–788.

News articles

• Global water crisis will intensify with climate breakdown, says report by Fiona Harvey, The Guardian, 17 August 2021. Climate change will greatly exacerbate water scarcity, with big changes predicted in the global water cycle.
• More than 3 billion people affected by water shortages, data shows by Fiona Harvey, The Guardian, 26 November 2020. Billions face hunger prompted by a growing shortage of water.
• 'This Is a War': Cross-Border Fight Over Water Erupts in Mexico by Natalie Kitroeff, The New York Times, October 14, 2020. Dwindling water resources are pushing people toward conflict.
• From Not Enough to Too Much, the World's Water Crisis Explained by Stephen Leahy. National Geographic, March 22, 2018. Lots of facts, figures, and infographics in this detailed survey.
• Two-Thirds of the World Faces Severe Water Shortages by Nicholas St. Fleur. The New York Times, February 12, 2016. Four billion people are short of water for at least one month a year, new research shows.
• Access to clean water and sanitation around the world—mapped by Katherine Purvis. The Guardian, 1 July 2015. An excellent interactive map of world water supply and sanitation problems.
• Why fresh water shortages will cause the next great global crisis by Robin McKie. The Guardian, 8 March 2015. Another look at the world's water crisis, with a great infographic.
• What does the Arab world do when its water runs out? by John Vidal. The Guardian, 20 February 2011. Dwindling water supplies will lead to growing political instability.
• Plan for China's Water Crisis Spurs Concern by Edward Wong. New York Times, 1 June 2011. Is greater abstraction from rivers the solution to a lack of water, or will it create other problems?
• Water scarcity: A looming crisis? by Alex Kirby. BBC News, 19 October 2004. An old article, but still a good quick summary of the issues at the heart of the pressing water crisis.
• Water: A running archive of world water stories from The New York Times.