Water Prospects In The 21st Century

Access to water is one of the pressing global issues of the 21st century. As our global population grows and becomes wealthier, the demand for water will greatly increase.

At the same time, water availability and quality are also under growing stress from climate change, energy scarcity, land use decisions, and the requirements of industry and minerals processing.

We will need to find better ways to both manage our current use of fresh water and configure it for the future, so as to be able to serve our growing populations and preserve stocks for future generations.

Water metrics

The world’s 6.7 billion people consume about 4,500 km3 (4.5 teralitres) of freshwater annually, roughly 10% for domestic use, 70% for food production, and 20% for industrial purposes. This total represents less than 5% of that which is annually available through precipitation.

On a global scale, freshwater makes up only about 2.5% of all the water on Earth, or around 35 million km3 (1 km3 = 264.2 x 109 U.S. gallon). Of this, 95% is fixed in glaciers and ice caps (for now), or found deep underground (less than 1 km below the surface). The remaining 2.5% falls onto the land as rain, of which only about 24% enters the rivers and streams and is accessible as surface water.

Further, a large portion of that precipitation falls in remote areas, leaving only 10% of the total continental precipitation input as easily available for human use (about 9,000–12,000 km3).


Three significant factors impact negatively on the local availability of freshwater. Firstly, climate change induced glacier shrinkage is decreasing the availability of glacial water, threatening groundwater resources with salination due to sea level rises, and endangering forests (which store vast quantities of water), especially through increased wild-fires.

Secondly, growing populations and rapid urbanisation raise water demand due to higher consumption patterns. Thirdly, modern lifestyles promote activities such as high meat consumption that result in the use of large amounts of freshwater. The same is true of some traditional cultures with rice production.

So while we face ever-growing demand for water on the one hand, we face severe supply constraints on the other. Research conducted by the World Resources Institute has found that 41% of the world’s population or 2.3 billion people live in areas subject to frequent water shortages. These are defined as water stressed areas, where per capita water supply is below 1,700 m3 (1,700,000 litres) per year.

Water = energy

Water is almost universally obtained thanks to the use of energy. Energy is used to drill for water, to extract it from wells or surface water bodies, to pump it to water treatment facilities, to filter and purify it, and to convey it to the user. 

The amount of energy required can be quite large if long distances are involved, and sometimes water travels hundreds of kilometres from source to consumer.

Conversely, water is essential in the production of some types of energy. One particular need is for cooling water in thermoelectric power stations and this need is set to grow substantially.

The use of footprinting for water and energy use will help increase understanding of the energy–water nexus. Footprinting can be a good way to compare different alternatives in terms of water or energy requirements, and may help decision makers choose what technologies or strategies to support.

Indeed, much water could be saved with substantial shifts toward low water-consuming types of energy facilities, such as wind and solar energy. The first attempts to measure footprints are available, but there is an obvious need for more data.

Sustainable water management should also consider the natural water cycle, with particular focus on soil and groundwater. Another progressive approach is to begin planning, particularly in urban centres, to separate supplies for drinking water and other purposes.

The centralization of water supply and treatment reduces the risks of operation and maintenance failures, making public management easier. This should include closer management of water, with closed loops in industrial processes. In addition, rainwater harvesting, separate collection of wastewater streams, and recycling of water offer better planning options for the future.

Virtual water

A further complicating factor in supply-demand analysis is the trade in virtual water, in which water is used in one place (e.g., a region or a country) to produce commodities exported for use elsewhere. Virtual water is especially important in the world agricultural trade and may be the major reason why “water wars” that have often been predicted have generally failed to materialize. Tony Allan, a social scientist at King’s College London has found that, as countries become richer, they require more water overall, but can now afford to import food to make up the shortfall.

In any event, the trade in virtual water complicates sustainable water management, because it introduces factors that are largely outside the control of the water planners and governments attempting to supply enough water in one form or another to satisfy anticipated water demand on the level of a watershed or an unknown region.

Future flows

Sustainable water management requires striking a balance between supply and demand, between the next year and decades into the future, between water quantity and water quality. These are momentous challenges, but they are not unfamiliar to water management specialists.

We now recognize that those complications are only part of the story, because constraints can also arise from the interactions of water provisioning with the provisioning of other resources: energy, land, and mineral resources among them.

These links present new hurdles for sustainable water management, requiring interaction across scientific disciplines and governmental entities. Addressing these issues will be very difficult, but ignoring them is likely to guarantee failure in water management as the dynamic 21st century unfolds.

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This article is based on Chapter 17, “Stocks, Flows and Prospects of Water” of an upcoming book: Linkages of Sustainability, edited by Thomas E. Graedel and Ester van der Voet (2010) and published by Massachussetts Institute of Technology Press. You can find the full list of authors by downloading the chapter from the link above. This book catalogues the results of the Ernst Strüngmann Forum (http://fias.uni-frankfurt.de/esforum/), which was convened in Frankfurt in 2008.