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Deep below the earths' surface the waters flow in the dark. No one ever witnesses the mysterious swirling, nor does anyone ever hear the mighty waters as it flows silently by. The underground water surges with energy and its own life-giving force, yet no living thing exists there. Sometimes the water is a mighty river, sometimes it is trapped in cracks and fissures in the rock. At times it lies still in secret underground caves, water dripping from above when it rains. It lurks there in the depths like a prowling predator, quietly, only to erupt in a white plume when its hiding place is discovered.

Groundwater is the inspiration for mystery and mysticism for some; it is in fact a crucial component of fresh water that sustains life on earth. In South Africa, groundwater accounts for only 13% - 15% of total water consumption. What makes this significant is the fact that around 65% of the population and 300 towns are completely dependent on groundwater for their existence (Colvin et al, 2008; WRC, 2005). In the US, almost half of the drinking water and 40% of irrigation water is pumped from aquifers, of which 30% is pumped solely from the world's largest known aquifer, the Ogallala Aquifer. Around 96% of rural areas and 20% urban areas in the US depend solely on groundwater for drinking water (Miller, 2000). Groundwater has the added benefit that it is usually filtered by rock through which it flows and delivers better-tasting drinking water WRC, 2005).

Underground water is contained in aquifers, that is, porous, water-drenched layers of sand, gravel or bedrock. Water movement in these aquifers is so slow that it usually travels only one meter in a year from a point of high elevation and high pressure to a point of low elevation and pressure. Aquifers are often found very deep underground and were formed in some instances as much as tens of thousands of years ago. These aquifers are in fact non-renewable resources and abstraction from them can be considered water mining (Miller, 2000).

Aside from drinking water and irrigation, groundwater serves many other purposes in the hydrological cycle and greater earth system: water trapped inside limestone caves maintain cavity pressure and prevent subsidence of the surface (sink holes); underground water replenishes above-ground rivers and streams in times of water stress; it prevents intrusion of salt water into fresh water in coastal areas (Miller, 2000) and it maintains biomes, such as the fynbos biome in the southern and western Cape which is sustained by the Table Mountain Group Aquifer (CSIR, 2007).

Extraction of groundwater globally serves an important economic purpose. The Central Valley in California, the vegetable basket of the US, is sustained by water extracted from the Ogallala Aquifer. Saudi Arabia, northern Africa (Libya and Tunisia in particular), northern China, southern Europe, parts of Mexico, the Middle East, India an Thailand all rely heavily and groundwater extraction. In Saudi Arabia groundwater extraction is almost three times greater than recharge a rate at which this valuable resource, which is more valuable than oil, may run out within the next 50 years (Miller, 2000). In South Africa groundwater extraction in gold mining areas such as Carletonville has resulted in extensive surface subsidence.

South Africa's groundwater has been called liquid gold' or hidden treasure'. What makes groundwater such a valuable resource is that it can usually be developed in close proximity to an intended end-user and is relatively cheap to develop as a result (WRC, 2005). "There is no doubt that groundwater will play an increasingly strategic role in serving rural areas either as a stand-alone source, in conjunctive use schemes with surface water and as a bridg­ing supply, particularly to assist in drought management and possibly in terms of reducing the effects of climate change." (WRC, 2005)

As the volumes of freely available and relatively cheap clean drinking water on the globe become reduced (due to pollution and water wastage), alternative options for potable drinking water and water for industrial processes are becoming more prominent. One option is desalination of groundwater. At present around 7,500 desalination plants spread across 120 countries supply roughly 0,1% of the fresh water used by humans. Desalination is an electricity intensive process, which makes desalinated water three to five times more expensive than water of conventional origin (Miller, 2000). Despite the high cost, desalination is useful for irrigation in coastal arid areas such as Saudi Arabia. Instead of importing wheat, Saudi Arabia uses desalinated water to produce its own wheat, albeit at seven times the world price per bushel (Miller, 2000).

The potential of groundwater as a resource has not been fully developed yet. It is imperative to understand the dynamics of a region's under ground water systems before embarking on large-scale extraction from aquifers. This resource can be extremely useful in dampening the effects of climate change and the global water crisis, but like any ecological resource it can be over-exploited, which could lead to more severe consequences for communities and industries that depend on it for their fresh water needs.

References:

Colvin, C., Maserumule, R., Woodborne, S., 2008: How does climate change affect groundwater in South Africa? CSIR: Natural Resources and the Environment.

CSIR e-news, 2007: Ecological impacts of groundwater abstraction investigated. www.csir.co.za/enews/2007_dec/ nre_04.html

Miller, 2000: Living in the Environment. Brooks/ Cole Publishing Company, USA.

Water Research Commission, 2005: The Water Wheel Nov/Dec 2005. Groundwater Assessment.http://www.wrc.org.za/archives /waterwheel%20archive/nov-dec% 2005/groundwater%20p14-17.pdf

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