Groundwater development has significantly increased during the last 50 years in most semiarid or arid countries of the world (Shah, 2004; Deb Roy and Shah, 2003). This development has been mainly undertaken by a large number of small (private or public) developers, with minor, if any at all, scientific, administrative or technological control. This is why some authors consider this new phenomenon as a si/ent revolution (Llamas and Martínez-Santos, 2005a,b). In contrast, the surface water projects developed during the same period are usually of larger dimension and have been designed, financed and constructed by government agencies, which also take on management and control, whether for irrigation or urban public water supply systems. This historical situation has often produced two effects: (i) most regulators have limited understanding and poor data on the groundwater situation and value; and (ii) in some cases the lack of control on groundwater development has caused serious problems that are later on reviewed in detail.

Spain, as the most arid country in Europe, is no exception to these trends. In Spain, and almost everywhere else, these problems have been frequently magnified or exaggerated by groups with lack of hydrogeological know-how, professional bias or vested interests (Llamas et a/., 1992). For instance, the World Water Council (2000, p. 13) states: 'Aquifers are being mined at an unprecedented rate - 10% of world's agricultural production depends on using mineral groundwater'. However, this 10% estimation is not based on any reliable data. In recent decades, the term groundwater overexploitation has become a pervasive and confusing concept, almost a kind of hydromyth, that has flooded the water resources literature. A usual axiom derived from this confusing paradigm or hydromyth is that groundwater is an

©CAB International 2007. The Agricultural Groundwater Revolution: 266 Opportunities and Threats to Development (M. Giordano and K.G. Villholth)

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