A third of the world's population lives in water-stressed countries now, and by 2025 this will probably have risen to two-thirds.
One person in six does not have access to clean water
Can we solve the world's water problems, and, if so, how? Views differ - although most agree water scarcity is a complex issue with no simple solution.
A range of water experts explain ways in which the private sector, international trade and technology might help.
Dr Lyla Mehta, Institute of Development Studies
Optimists' view: The global system will be able to cope
Professor Tony Allan, King's College London/SOAS Water Research Group
Water pessimists are wrong but useful - water optimists are right but dangerous.
Water pessimists are useful because they raise the urgency of water issues. Water optimists on the other hand encourage the natural human tendency to ignore a problem that has never been encountered in 5,000 years of managing water.
The serious water deficits in arid regions can be addressed by the global hydrological and trading systems.
Ninety percent of the water needed by an individual - or economy - is required to raise their food. The 10% of freshwater needed for domestic and non-agricultural jobs is almost always available locally. Where there are deficits desalination has become an economic option - although populations at high elevations face problems.
The global system will be able to cope because the future world population will level off at around nine billion. Food production systems are becoming more efficient and will be able to meet the needs of the less than 50% increase in future consumers.
Poverty is the main problem for users needing adequate water for food and other basic needs. But poverty determines water poverty - water poverty does not determine poverty.
The diversification of economies will solve the water problems of poor countries - especially in Africa.
Virtual water: Trade is already helping
Paul van Hofwegen, Senior Water Management Expert, World Water Council
Virtual water is the amount of water used in the production process and therefore "contained" in a product. With the trade of food crops or any commodity, there is a virtual flow of water from producing and exporting countries to countries that consume and import those commodities.
Virtual water trade is already a silent alternative for most water-scarce countries.
The growing interest in virtual water comes from the fact that it could be used as an instrument to achieve water security in water-poor regions.
But most of all, it is because of its increasing importance for food security in many countries experiencing a continuous expansion of their population.
At the same time, food security is politically a very sensitive subject. A government cannot afford to put its population at risk and abandon their food sovereignty.
A virtual water import policy increases dependency between countries. This is both a stimulant for co-operation and peace - and a risk at the same time.
Reaching the poor: Small providers play a key role
Anne Bouvier, Policy Officer, WaterAid
WaterAid believes that everyone should have access to safe, affordable water and sanitation.
The key question is how to reach the 1.1 billion people without safe water and the 2.6 billion people without sanitation.
The big debate is currently focused on international private providers. But, because of the risks they perceive, many of these are actually pulling out of developing countries.
Meanwhile, many millions of urban dwellers use small and medium providers for their water. These providers often sell over-priced water which can be of dubious quality.
Their role must be acknowledged and their services must be regulated so that they provide an affordable, safe and reliable service for the poorest.
To enable this to happen, water sector reform is vital. Local people must be involved in decision making and the sector must be overseen by capable public institutions.
Private sector: A strong but limited player
Dr Alan Nicol, Water Policy Programme, Overseas Development Institute
Insofar as water scarcity is a physical phenomenon then the private sector can play a contracting role, helping to establish more efficient service delivery systems, reducing leakage in domestic networks or improving irrigation efficiency.
However, if scarcity is a social phenomenon where allocation decisions involve trade-offs between, say, water for irrigated agriculture versus more "serviced" urban populations, then the private sector has little role to play in what is essentially a political process.
Finally, the private sector may help to alleviate scarcity of innovation and knowledge in coping with fluctuations in water availability through capacity building and knowledge development within relevant institutions.
Public systems: Need revitalising for the poorest
Dr Lyla Mehta, Institute of Development Studies, University of Sussex
Calls to enhance the role of the international private sector in providing water to the poor have turned out to be misplaced.
My research shows that water shortages are the result of a combination of institutional, ecological and socio-political factors. Solutions therefore cannot be simplistic.
Where the private sector has been involved with the provision of water, price hikes have often led to disconnections for the poorest of the poor. Regulatory frameworks are usually absent.
Global water utilities are also pulling out from poor countries due to the protests of local people and the high financial risks involved.
But public systems, which make up the bulk of water provision, still suffer from inadequate financing and poor maintenance, and unregulated vendors continue to charge exorbitant rates in poor areas.
While the private sector can help in some areas, the poorest of the poor need revitalised and reformed public systems which do not emphasise profits, but instead focus on enhancing poor people's entitlements and rights to water.
Send us your views.
I am in South Africa examining the impacts of a cost recovery policy in respects to the delivery of affordable water. Communities where I have visited are having pre-paid water meters installed; under which if they cannot pay they cannot obtain water. Many people blame overpopulation for stressing our natural resources but it is also necessary to examine over consumption of resources and an economic system that perpetuates unsustainable use of such resources. The response to water scarcity to trade virtual water is a frightening one because it doesn't address the issue of equitable access and only leads us farther into a vast desert where only those who can afford to live in a high security oasis.
Berkley Carnine, Eugene, United States
While population growth and the total number of people now occupying our little planet is a major cause for concern, the level of resource consumption in westernised or developed countries is also a serious issue. Water is but one of many factors in need of attention - along with energy (the need for renewable development), economics (restructuring the third world debt so countries are not crippled and no longer support our luxurious lifestyles at their expense), agriculture (and its use of chemicals, water and generous government subsidies) and transport (ever bigger, less economic vehicles).
I believe it is important to make genuine efforts to improve the quality of people's lives in developing countries, but it is also important for those nations to educate their population, thus allowing growth and change to occur continually. Supplying the most basic of needs - drinking water and sanitation - is the first step; combined with hygiene education. While many methods exist for supplying water, it does not appear prudent to state one method as the best - numerous factors affect water abstraction and supply and each case and each situation should be viewed on its own merits, however I maintain a focus should be placed on fulfilling the needs of the local population and developing technologies that poorer nations will be able to install, manage and receive long term benefit from.
In most countries where water is plentiful and clean - it was not until a household charge for this water was introduced - that the population had water supply security.
Howard Scott, Auckland, New Zealand
Water access mirrors inequalities within societies. In places where women and poor people aren't important, their water needs - for livelihoods or drinking water- are very unlikely to be met. There is a growing appreciation that because of population growth, water is a resource that must now be managed: allocation, pollution regulation, well maintained adequate infrastructure, functioning institutions - it's not rocket science. Technology helps but there are few quick fixes.
Margaret Catley-Carlson, Canada & New York
Why is it that everyone plays ostrich and sticks their head in the sand when it comes down to admitting that most of today's food and water problems are only problems because of the rapid growth of the world's human population? Just because tackling population growth (and preferably reduction) is a very difficult issue - that is no reason for ignoring it. All the fine words in this article and others about providing adequate, clean water are a total waste of time if the population issue is not headlined and slated for urgent action.
Tony Marshallsay, Riyadh, Saudi Arabia
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