85% of the world population lives in the driest half of the planet.
783 million people do not have access to clean water and almost 2.5 billion do not have access to adequate sanitation. 
6 to 8 million people die annually from the consequences of disasters and water-related diseases.
Various estimates indicate that, based on business as usual, ~3.5 planets Earth would be needed to sustain a global population achieving the current lifestyle of the average European or North American.
Global population growth projections of 2–3 billion people over the next 40 years, combined with changing diets, result in a predicted increase in food demand of 70% by 2050.
Over half of the world population lives in urban areas, and the number of urban dwellers grows each day. Urban areas, although better served than rural areas, are struggling to keep up with population growth (WHO/UNICEF, 2010).
With expected increases in population, by 2030, food demand is predicted to increase by 50% (70% by 2050) (Bruinsma, 2009), while energy demand from hydropower and other renewable energy resources will rise by 60% (WWAP, 2009). These issues are interconnected – increasing agricultural output, for example, will substantially increase both water and energy consumption, leading to increased competition for water between water-using sectors.
Water availability is expected to decrease in many regions. Yet future global agricultural water consumption alone is estimated to increase by ~19% by 2050, and will be even greater in the absence of any technological progress or policy intervention.
Water for irrigation and food production constitutes one of the greatest pressures on freshwater resources. Agriculture accounts for ~70% of global freshwater withdrawals (up to 90% in some fast-growing economies).
Economic growth and individual wealth are shifting diets from predominantly starch-based to meat and dairy, which require more water. Producing 1 kg of rice, for example, requires ~3,500 L of water, 1 kg of beef ~15,000 L, and a cup of coffee ~140 L (Hoekstra and Chapagain, 2008). This dietary shift is the greatest to impact on water consumption over the past 30 years, and is likely to continue well into the middle of the twenty-first century (FAO, 2006).
About 66% of Africa is arid or semi-arid and more than 300 of the 800 million people in sub-Saharan Africa live in a water-scarce environment – meaning that they have less than 1,000 m3 per capita (NEPAD, 2006).
The impact of climate change
The IPCC predicts with high confidence that water stress will increase in central and southern Europe, and that by the 2070s, the number of people affected will rise from 28 million to 44 million. Summer flows are likely to drop by up to 80% in southern Europe and some parts of central and Eastern Europe. Europe’s hydropower potential is expected to drop by an average of 6%, but rise by 20–50% around the Mediterranean by 2070 (Alcamo et al., 2007).
The cost of adapting to the impacts of a 2°C rise in global average temperature could range from US$70 to $100 billion per year between 2020 and 2050 (World Bank, 2010). Of this cost, between US$13.7 billion (drier scenario) and $19.2 billion (wetter scenario) will be related to water, predominantly through water supply and flood management.
A resource without borders
Water is not confined to political borders. An estimated 148 states have international basins within their territory (OSU, n.d., 2008 data), and 21 countries lie entirely within them (OSU, n.d, 2002 data).
There are 276 transboundary river basins in the world (64 transboundary river basins in Africa, 60 in Asia, 68 in Europe, 46 in North America and 38 in South America).
185 out of the 276 transboundary river basins, about two-thirds, are shared by two countries. 256 out of 276 are shared by 2, 3 or 4 countries (92,7%), and 20 out of 276 are shared by 5 or more countries (7,2%), the maximum being 18 countries sharing a same transboundary river basin (Danube).
46% of the globe’s (terrestrial) surface is covered by transboundary river basins.
148 countries include territory within one or more transboundary river basins. 39 countries have more than 90% of their territory within one or more transboundary river basins, and 21 lie entirely within one or more of these watersheds.
Russian Federation shares 30 transboundary river basins with riparian countries, Chile and United States 19, Argentina and China 18, Canada 15, Guinea 14, Guatemala 13, and France 10.
Africa has about one-third of the world’s major international water basins – basins larger than 100,000 km2. Virtually all sub-Saharan African countries, and Egypt, share at least one international water basin. Depending on how they are counted, there are between 63 (UNEP, 2010b) and 80 (UNECA, 2000) transboundary river and lake basins on the African continent.
Rich nations are tending to maintain or increase their consumption of natural resources (WWF, 2010), but are exporting their footprints to producer, and typically, poorer, nations. European and North American populations consume a considerable amount of virtual water embedded in imported food and products. Each person in North America and Europe (excluding former Soviet Union countries) consumes at least 3 m3 per day of virtual water in imported food, compared to 1.4 m3 per day in Asia and 1.1 m3 per day in Africa (Zimmer and Renault, n.d.).
Land grabbing is another increasingly common phenomenon. Saudi Arabia, one of the Middle East’s largest cereal growers, announced it would cut cereal production by 12% a year to reduce the unsustainable use of groundwater. To protect its water and food security, the Saudi government issued incentives to Saudi corporations to lease large tracts of land in Africa for agricultural production. By investing in Africa to produce its staple crops, Saudi Arabia is saving the equivalent of hundreds of millions of gallons of water per year and reducing the rate of depletion of its fossil aquifers.
Nearly all Arab countries suffer from water scarcity. An estimated 66% of the Arab region’s available surface freshwater originates outside the region.
Pollution
The treatment of wastewater requires significant amounts of energy, and demand for energy to do this is expected to increase globally by 44% between 2006 and 2030 (IEA, 2009), especially in non-OECD countries where wastewater currently receives little or no treatment (Corcoran et al., 2010).
Pollution knows no borders either. Up to 90% of wastewater in developing countries flows untreated into rivers, lakes and highly productive coastal zones, threatening health, food security and access to safe drinking and bathing water Over 80% of used water worldwide is not collected or treated (Corcoran et al., 2010).
Cooperation, a contrasted reality
There are numerous examples where transboundary waters have proved to be a source of cooperation rather than conflict. Nearly 450 agreements on international waters were signed between 1820 and 2007 (OSU, 2007).
Over 90 international water agreements were drawn up to help manage shared water basins on the African continent (UNEP, 2010).
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