Planet Earth is seemingly awash with water – we call it 'the Blue Planet'.

But how much accessible fresh water is there?

Very little.

Only 2.5% of all the water on Earth is fresh water and more than 97% is saltwater.

Of this 2.5% of fresh water, more than two-thirds (68.7%) is frozen as snow and ice, and more than one-third is stored below ground as groundwater. This means that only 0.3% of all fresh water on the planet is readily available as surface water in lakes, swamps, rivers and streams (Gleick, P. H., 1996: Water resources. In Encyclopaedia of Climate and Weather).

It’s remarkable to think that the global population and all living species are supported by such a small amount of all the water on the planet! For how much longer will this be the case?

Water is constantly circulating around the planet in a system called the ‘hydrological cycle’. Water evaporates from surface storage like oceans, lakes, ponds and rivers. It cools as it rises, condenses to form clouds and eventually returns to Earth’s surface as precipitation – rainfall, snow or hail. Water can be stored in snow and ice for hundreds of years and if it enters the groundwater system may stay there for thousands of years. As well as rainfall, groundwater systems sustain lakes and rivers and act as a reliable water source for many regions around the world.

Click for more information on the water cycle and freshwater resources.

The Earth’s complex climate system means that water isn’t distributed evenly across the world. Different regions experience higher or lower precipitation levels and seasonal variations. This variation is a major cause of the presence of different ecosystems across the planet.

From a human perspective, it also means that water is often in the wrong place, in the wrong form or available at the wrong time.

This is because water availability depends on:

  • The amount of water a country or region has – e.g. precipitation, the presence of rivers or lakes and groundwater stores.

  • The number of people and uses that water has to support – their individual demand/consumption of that water.

Although the absolute quantities of fresh water on earth have always remained approximately the same, the uneven distribution of water and human settlement continues to create growing problems of fresh water availability and accessibility. Uncertain water availability is a challenge faced by a growing number of countries, and one that can impact upon economic growth.

Water scarcity occurs when the amount of water withdrawn from lakes, rivers or groundwater is so great that water supplies are no longer adequate to satisfy all human or ecosystem requirements, resulting in increased competition between water users and other demands.

This map compares water supply in river basins from 1995 to 2025. Looking more closely, it also illustrates sub-regional variations in water supply. For example, in the UK, the south east is noticeably more water scarce than the rest of the country. Similar variations occur in many countries throughout the world, such as Turkey, India, Australia and the U.S. We can also see that some areas of greatest predicted water scarcity are also those with the highest populations, parts of India, China, Nigeria, Egypt and the U.S.

Q. Can you see any striking differences in water supply in particular areas over this 30 year period? What might be the reasons for this?
Q. What concerns you about the patterns this map shows? Why?

By 2050, nearly half of the world’s population will be living in areas where water is scarce yet 90% of all population growth will occur in those regions.

Look at the Taking Action pages for ideas on how you can reduce your impact on freshwater systems now and in the future.

Although we are viewing water availability in terms of human needs, it is also a vital requirement for all living things and the ecosystems that support them, and us, through ecosystem services. More than 1.4 billion people are now living in river basins where modest environmental water requirement levels are already in conflict with current water use, and this number is growing (Smakhtin, V.; Revenga, C.; and Döll, P. 2004).

If we assume a need to satisfy this ecological water requirement, this is likely to exacerbate the human water scarcity. Which leaves us with a future dilemma – does the human requirement for water (for all our ‘needs’, not just basic drinking and sanitation) outweigh the ecological? And if so, at what cost in the long-term?

Globally, not only do we rely on less than 1% of the total fresh water to support an estimated 7 billion people worldwide, but the accessible water is unequally distributed.

For more detailed information on the Earth’s natural water cycles and availability of freshwater resources see: The World Water Development Report 3, Chapter 10.

For more information on environmental water requirements see the report: Taking into Account Environmental Water Requirements in Global-scale Water Resources Assessments.