The world’s groundwater resources

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Importance of groundwater

Groundwater systems are replenished by precipitation and surface water and discharge into surface waters, the ocean or by evapotranspiration back in the atmosphere. Groundwater circulation globally is less than atmospheric and surface waters but what is stored beneath the earth's surface is orders of magnitude larger. Its total volume represents 96% of all earth's unfrozen fresh water 1.Without groundwater, the face of the earth would look different. Groundwater feeds springs and streams, supports wetlands, maintains land surface stability in areas of unstable ground and overall is a critical water resource serving mankind's water needs 2.For example, it meets over 75% of the water needs in Estonia, Iceland, Russian Federation, Jamaica, Saudi Arabia, Georgia, Swaziland, Mongolia, Libya and Lithuania. Figure 4.9.1 reflects intensity of groundwater abstraction in different countries: particularly high (per km2) groundwater abstractions occur in Bahrain, Taiwan, Mauritius, Malta, Pakistan, Bangladesh, India and Israel. Figure 4-9-2 shows the extent groundwater is allocated to agricultural, domestic and industrial use. Box 4-9-1 lists the 10 countries in the world with largest groundwater abstraction. About 60% of groundwater withdrawn is used by agriculture; the rest is almost equally divided between the domestic and industrial sectors. The predominant use is agriculture in many countries where arid and semi-arid climates prevail3 . Predominantly industrial sector use is in a few countries only. In many nations, more than half of the withdrawn groundwater is for domestic water supplies and globally it provides 25 to 40 % of the world's drinking water4. Today, half the world's megacities and hundreds of other major cities on all continents rely upon or make significant use of groundwater. Small towns and rural communities particularly rely on it for domestic supplies. Even where groundwater provides lower percentages of total water used, it still may serve local areas where otherwise no other accessible supply exists and it usually does so with relatively low cost and good water quality. Finally, groundwater bridges water supply gaps during long dry seasons and during droughts.