International Hydrological Programme on World Water Day 98
The theme for the World Day for Water for 1998 was: Ground water, the invisible resource, focusing on the quality of water as well as on the quantity. Ground water is also one of the two priority themes being developed by the Fifth Phase of the IHP (1996-2001). Please find below a text prepared by the International Hydrological Programme which was included in the kit for World Day for Water. This text highlights the main features of ground water and its importance for meeting the water resource needs of humanity.
Resources
Ground water represents around 30% of the freshwater resources of the earth, while lakes and rivers correspond to less than 1% and the largest volume of fresh water is stored in glaciers (69%).
Ground water is one of the components of the hydrological cycle, stored underground in geological layers called aquifers; it is a result of infiltration of rainfall and surface water (rivers) with which it maintains a close relationship. Aquifers present the advantage of having large to huge volume storage capacity with a very low flow and are easily accessed through dug-wells or bore holes, either pumped or flowing (artesian wells) or through springs. The importance of aquifers depends on the geological nature of the layers: for example, sedimentary formations represent good aquifers while hard rocks have a limited capacity for storage.
Distribution
Ground water is unequally distributed throughout the world depending on different climatic conditions: temperate zones with significant rainfall provide an important renewable recharge to aquifers which play an important role together with surface water, ensuring a good inter-annual regulation in case of drought; arid zones with scarce rainfall and resulting intermittent rivers receive less renewable recharge but ground water constitutes the predominant water resource, and sometimes the only water resource, in desert areas where it is stored in fossil aquifers.
Infiltration of rainfall and surface water through porous layers provides good quality ground water in general; this added to easy access of groundwater in several regions of the earth explains the large use of ground water for human water supply covering more than 60% of human needs. Ground water also ensures between 20% and 40% of industrial water needs in industrialized countries. In arid zones, it often represents the main water source for agriculture (40% in India, 80% in Saudi Arabia).
Management
Ground water is however threatened by several factors related to its mismanagement. It is often over-exploited especially in arid zones and a lowering of the water table is thus induced entailing an increase in pumping costs and the possibility of contamination by salt water especially in coastal zones where aquifers are threatened by sea water encroachment. Groundwater might also be polluted by sewage discharged into rivers or by agricultural practices; it is very difficult and costly to recover the initial characteristics of groundwater after pollution.
A valuable resource for humanity, groundwater should be well managed and protected to ensure sustainable use for domestic consumption as well as industry and agriculture. The assessment of available aquifer resources is a prerequisite for rational groundwater management. Rational management is the key to sustainable use of ground water and should be closely linked, when possible, to surface water management in an integrated approach at the level of watersheds, regions and countries. Fossil aquifer exploitation corresponds to mining exploitation and should be carefully planned to ensure longevity. Ground water should be protected from pollution by controlling the quality of river water and polluting deposits. In order that all the above-mentioned factors may be heeded a water legislation policy on a country-wide scale must be defined to establish rules for prospection and use of ground water as well as its protection against pollution. All aspects related to the management and protection of ground water should be made known to the public which should be encouraged to participate in its protection.