Water Resources

The fact that water is a resource may come as a surprise to some people. It is often taken for granted, because for many people, water comes from a tap. But that is really not where it comes from. All water on Earth is part of the hydrological cycle.

The sun constantly evaporates all water on Earth (lakes, rivers, seas, and oceans) into the atmosphere. Some of that water is returned as precipitation-rain or snow. While part of this precipitation evaporates back into the atmosphere, some of it drains into lakes and rivers, starting the long journey back to the sea. Along the way, some will filter through the ground to become soil moisture or groundwater. It may collect in underground rivers called aquifers. Or it may, through dramatic shifts in geology have become trapped permanently. Under normal conditions, groundwater works its way back into surface water, becoming the main source of river flow. Some of the soil moisture will be incorporated by plants, which will in turn release some water back to the atmosphere through transpiration. This is the hydrological cycle.

The International Hydrological Programme, UNESCO's intergovernmental scientific co-operative programme in water Resources, is a vehicle through which Member States can upgrade their knowledge of the water cycle and thereby increase their capacity to better manage and develop their water resources. Read more.

Through this cycle, enormous amounts of water move around the globe. Some of this movement is rapid, in the case of water in rivers or the atmosphere, but some of it is slow. Water in a glacier can take centuries to move and in deep aquifers, tens of thousands of years may be required. Paleowater, water that has been trapped in an underground formation since prehistoric times, does not move at all.

Understanding water resources, where the water comes from, how it moves, what its characteristics are, is vital to its proper management.

Knowledge of the hydrological regime of a region is a vital prerequisite for
all work in hydrology and the development of water resources.
The World Meteorological Organization has launched a series of initiatives
tocollect the data and information key to successful development.
Read more.

In addition to natural processes, each day, human activities make heavy withdrawals from the water balance. But as we can see from the hydrological cycle, water is a limited, though renewable, resource. Much of the water on Earth, almost 98%, is salty. This means that the humans, agriculture, industry, plants, and wildlife, all compete for less than 3% of freshwater, much of which is frozen in the glaciers of Antarctica and Greenland.

Fortunately there are many efforts made to understand the availability of water, so that we do not, collectively, overdraw on the water balance. For example, many countries have programmes to measure the hydrological elements that influence how much water is available, such as rates of precipitation, evaporation, and river flow. A network of global hydrological measuring stations in nearly 200 countries and territories provides a good, but nevertheless incomplete picture of the world's water resources. Despite the large total number of stations (over 194,000 were measured precipitation in 1994 according to the World Meteorological Organization), there are serious gaps in the developing world, where the need for water data is the greatest. The cost of such measuring stations is not the only obstacle. Governments around the world are willing to invest huge sums to extract water through dams, canal systems, and deep wells, but not the tiny fraction needed to gather vital hydrological needed ensure that the project is viable over the long term.

The International Atomic Energy Agency is using isotope hydrology to help improve knowledge of ground water resources in Ethiopia.

Quality data are the foundation on which sustainable water projects are built. If we are to be able to respond to growing demands for water expected in the future, from increased population, more intensive farming to feed more people, and increased urbanization, efforts to improve our knowledge of water will have to be strengthened, and soon. For such understanding of water resources will become even more important to making the right decisions about water management in the future.