Context - Water is essential for human survival and well-being and important to many sectors of the economy. However, resources are irregularly distributed in space and time, and they are under pressure due to human activity.
How can water resources be managed sustainably while meeting an ever increasing demand?
Around the world, human activity and natural forces are reducing
available water resources. Although public awareness of the need to
better manage and protect water has grown over the last decade, economic
criteria and political considerations still tend to drive water policy
at all levels. Science and best practice are rarely given adequate
Pressures on water resources are increasing mainly as a result of
human activity – namely urbanisation, population growth, increased
living standards, growing competition for water, and pollution. These
are aggravated by climate change
and variations in natural conditions.
Still, some progress is being made. More and more, officials are
evaluating water quantity and quality together, and coordinating
management efforts across borders.
The world’s water exists naturally in different forms and locations:
in the air, on the surface, below the ground, and in the oceans.
Freshwater accounts for only 2.5%
of the Earth’s water, and most of it is frozen in
ice caps. The remaining unfrozen
freshwater is mainly found as
groundwater, with only a small
fraction present above ground or in the air.
Looking at how water moves through the Earth’s
helps us understand how it interacts with the environment and how much
is available for human use.
2.1 Precipitation – rain, snow, dew etc. – plays the key
role in renewing water resources and in defining local climatic
conditions and biodiversity.
Depending on the local conditions, precipitation may feed rivers and
lakes, replenish groundwater, or
return to the air by evaporation.
2.2 Glaciers store
water as snow and ice, releasing varying amounts of water into local
streams depending on the season. But many are shrinking as a result of
River basins are a useful “natural unit” for the
management of water resources and many of them are shared by more than
one country. The largest river basins include the Amazon and Congo Zaire
basins. River flows can vary greatly from one season to the next and
from one climatic region to another. Because lakes store large amounts
of water, they can reduce seasonal differences in how much water flows
in rivers and streams.
Wetlands – including swamps, bogs, marshes, and
lagoons – cover 6% of the worlds land surface and play a key role in
local ecosystems and water
resources. Many of them have been destroyed, but the remaining wetlands
can still play an important role in preventing floods and promoting
Of the freshwater which is not
frozen, almost all is found below the surface as
Generally of high quality, groundwater is being withdrawn mostly to
supply drinking water and support farming in dry climates. The resource
is considered renewable as long as groundwater is not withdrawn faster
than nature can replenish it, but in many dry regions the groundwater
does not renew itself or only very slowly. Few countries measure the
quality of groundwater or the rate at which it is being exploited. This
makes it difficult to manage.
3. How much freshwater is available in different countries?
The quantity of freshwater that
is available to a given country without exceeding the rate at which it
is renewed, can be estimated taking into account the amount of
precipitation, water flows entering and leaving the country, and water
shared with other countries.
The average amount available per person varies from less than 50
m3 per year in parts of the Middle East to over 100 000
m3 per year in humid and sparsely populated areas.
The United Nations has kept a country by country database of such
estimates for several decades.
Though the database has become a common reference tool, it has some
drawbacks. Figures only indicate the maximum theoretical amount
available for a country and may be an overestimation. Moreover, annual
and national averages tend to mask local and seasonal differences.
Select a country to view the amount of water available in 2005:
If inadequately managed, activities like farming, forest-clearing,
road-building, and mining can lead to too much soil and suspended
particles ending up in rivers (sedimentation). This damages aquatic
ecosystems, impairs water quality
and hinders inland shipping.
Pollution can harm water resources and aquatic
ecosystems. Major pollutants
include for instance organic matter and disease causing organisms from
waste water discharges, fertilisers and
pesticides running off from
agricultural lands, acid rain
resulting from air pollution, and
heavy metals released by mining and
The effects of extracting too much water, both from surface waters and
groundwater, have been dramatic. A
striking example is the drastic reduction in size of the Aral Sea and
Lake Chad. Little is being done to address the causes, which include
poor water management practices and
In recent decades, much more water has been extracted from underground
sources. The benefits of withdrawing
groundwater are often short-lived,
while the negative consequences – lower water levels and depleted
resources, for example – can last a long time.
4.4 Climate change appears to
increase existing pressures, for example in areas already suffering from
water shortages. Land and mountain
glaciers are shrinking more rapidly
in recent years. Extreme weather events stemming from global warming,
such as storms and floods, are likely to become more frequent and
severe. However, based on current knowledge, scientists can only make
general predictions about the impact of climate change on water
Meeting a continuous and ever increasing demand for water requires
efforts to compensate for natural variability, and to improve the
quality and quantity available.
5.1 Rainwater has been collected for thousands of years
in many parts of the world. Today, this technique is used in Asia to
replenish underground supplies. It is relatively inexpensive and has the
advantage of allowing local communities to develop and maintain the
required structures themselves.
Diverting surface water into the ground can help
reduce losses from evaporation, compensate for variations in flow, and
improve quality. Middle East and Mediterranean regions are applying this
Dams and reservoirs have been built to store water
for irrigation and drinking. Moreover dams can provide power and help
control floods, but they can also bring about undesirable social and
Transferring water between river basins can also help
alleviate shortages. China, for instance, already has major interbasin
links, and is planning more. The impact of these projects on people and
the environment must be monitored closely.
Wastewater is now reused for different purposes in
many countries, especially in the Middle East, and this practice is
expected to grow. Worldwide, non-potable water is used for irrigation
and industrial cooling. Cities are also turning to water re-use to
supplement drinking water supplies, taking advantage of progress in
5.3 Desalinated water – seawater and other salty water
that has been turned into
freshwater – is used by cities and
by industries, especially in the Middle East. The cost of this technique
has dropped sharply, but it relies heavily on energy from
fossil fuels and hence raises waste
management and climate change
6. How could water resources be developed sustainably?
Using water resources sustainably
is challenging because of the many factors involved, including changes
in climate, the natural variability of the resource, as well as
pressures due to human activity.
At present, most water policy is still driven by short-term economic
and political concerns that do not take into account science and good
stewardship. State-of-the-art solutions and more funding, along with
more data on water resources, are needed especially in developing
To assess the state of our water resources, we must fully appreciate
the roles of different parts of the
– such as rain, meltwater from
glaciers, and so on. Otherwise, it
remains difficult to develop adequate protection and mitigation
Poor water quality and unsustainable use of water resources can limit
the economic development of a country, harm health and affect
livelihoods. On a positive note, more
sustainable practices are starting
to be adopted.
When managing water resources, more attention should be paid to
increasing existing natural resources and reducing demand and
The traditional response to rising demand for water was to store
surface water in reservoirs, divert flow to dry regions and withdraw
groundwater. Now these methods are
increasingly supplemented by water reuse, desalination and rainfall
harvesting. Certain regions are even going to the extreme of exploiting
non-renewable groundwater resources.
Some countries have programs to reduce demand and losses from urban
water distribution systems but more efforts are necessary. However, this
will involve changes in behaviour requiring education and political
commitment. Such efforts to conserve water and reduce demand are not
only useful in regions where water is in short supply, they can also
bring economic benefits in wetter regions.
Decentralised approaches to water resource management that focus on
river basins are increasingly pursued even across borders. Exchanging
information between countries that share river basins will yield both
economic and environmental benefits.
Our water resources are under pressure. More reliable information is
still needed regarding the quality and quantity of available water, and
how this availability varies in time and from place to place. Human
activities affect the water cycle in many ways, which needs to be
understood and quantified to manage water resources responsibly and
It has become evident that:
Changes in climate are affecting water availability
Pollution, water diversions and uncertainties about the
abundance of water are threatening economic growth, environment, and