Science for the twenty-first century

A New Commitment

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And not a drop to drink? The freshwater crisis

Between 1900 and 1995, world demand for water multiplied by six, twice the rate of population growth over the same period. According to a recent analysis1, the scarcity of water in localised areas will become the second most pressing concern in the 21st century (the first is population growth). At first sight, access to freshwater may seem to be a purely socio-economic issue - some people will have the water resources and/or the money to exploit them, others will not. But some applications of science - such as synthetic fertilisers, some industrial processes, intensive irrigation - are partly responsible for creating this imminent shortage. Other applications of science also offer some of the solutions.

Why will water availability become an issue in the coming decades?

- Freshwater is already a scarce resource. Over 70 percent of the surface of the Earth is covered by water, but only 2.5 percent is fresh water. The rest is salt water contained in the oceans. And of the already small proportion of freshwater, only 1 percent - less than 0.007 percent of all the water in the world - is easily accessible. This is the water found in lakes, rivers, reservoirs and those underground sources that are shallow enough to be tapped at an affordable cost. Only this amount is renewed regularly by rain and snowfall, and therefore available on a sustainable basis.

- Uneven distribution. Regions served by major rivers have a ready supply of water - although this can vary enormously between wet and dry seasons. The Amazon carries 16 percent of global river flow (or run-off). But arid zones, which cover 40 percent of the world's landmass, have only 2 percent of run-off.

- Food security. As population increases, so does the quantity of food needed to feed the planet. Since the 1960's, farmers have used intensive irrigation to meet this growing demand. Irrigation now accounts for 70 percent of all water withdrawals. In arid regions, irrigation can take up to 90 percent of available water resources.

- We are wasting water. In one sense, water is never lost - it simply changes from one state or place to another. But it takes 1400 years for an underground water table (called an aquifer) to be replenished.
  • In developing countries as much as 50 percent of drinking water is lost through leaks.
  • Intensive irrigation also wastes as much as 40 percent of the water withdrawn.
  • While each member of a family living in an arid area of Africa uses 10-40 litres of water a day for drinking, cooking and washing, an urban European or North American family uses 300-600 litres a day per person.


- Pollution. While industry returns most of the water it uses to rivers and lakes, it is often contaminated. And water drained off from irrigation usually contains fertilisers and pesticides that pollute groundwater sources and rivers. According to Andras Szollosi-Nagy, Director of UNESCO's Division of Water Sciences, water pollution is a time bomb. In European groundwater reserves, he says, the first aquifer layer is finished. The nitrate and phosphate concentration is so high that we will have to go down to the second level - if there is a second layer.

- Population growth. Population is expected to grow to 8.7 billion by 2025 - 2.6 billion more than in 1995. And this growth will be highest in those areas that already have moderate or high water stress. At present about 75 percent of the Earth's population live in regions where over 20 percent of available water resources are being used.

- Climate change. Many analyses forecast a 1° C to 2° C increase in air temperature by 2050 as a result of global warming. In arid regions this could result in a 10 percent drop in rainfall and a 40-70 percent reduction in the water available in rivers and lakes. In cooler regions at high latitudes, winter thaws could be more intense, causing flooding, while river levels would run low in summer.

How can science help offset a water shortage?
Much can be done to reduce water stress. Desalination of brackish water is one example. Andras Szollosi-Nagy sees potential for 'soft' solutions, that do not require structural engineering. Biotechnology could have a large part to play, he says. Genetically-engineered bacteria and micro-organisms could play a role in water purification, particularly for the huge masses of groundwater. They may be able to decompose contaminating compounds. Biotechnology could also produce new crops that require less water, or that can survive in arid conditions.

But, says Szollosi-Nagy, there is no vision for water resources management for the 21st century. With the World Water Council, UNESCO is starting a water management scenario analysis for the next 35 years. There is a lack of sufficient data, says Szollosi-Nagy, And the models we have are almost always calibrated using data from Northern America and Europe. Africa plays an important role in global circulation of atmospheric moisture, but there are no data. So the uncertainties which are associated with climate scenarios are extremely large. But, he says, the Internet could soon change this: With Internet technology, the cost of online observing systems and remote observing systems will drop to a couple of hundred dollars instead of a couple of hundred thousand dollars. All you need is a mobile telephone.

Scientists are also looking into the past to determine natural cycles of rainfall and water availability. Archives of the Venice floods, tax records, ship's logs, personal diaries and the records of amateur weather watchers are all being analysed.

In the meantime, there are ways to make better use of the water we do have:
  • Reducing losses - by repairing leaks, replacing intensive irrigation with drip irrigation (releasing water in droplets rather than in a steady stream)
  • Rainwater harvesting - collecting run-off from roofs and paved surfaces
  • Using waste water for industry
  • Education and information campaigns. Getting water on the international agenda of decision-makers, especially in water-stressed regions (and this includes Europe). In developing countries, women should be involved in water resource management. They are often most closely involved in water use.


1 See Colwell, R.R. & Sasson, A. Biotechnology and development. In World Science Report 1996. UNESCO













Edited and updated by UNESCO's Office of Public Information (OPI)