In the last half-century in most semi-arid or arid developed and developing countries, many aquifers have become intensively used. This means that the hydrogeological conditions may have changed, with groundwater storage being modified significantly. This intensive use has been performed mainly by millions of modest farmers with scarce public or governmental planning. This silent revolution has been market driven. The cost of groundwater abstraction is usually a small fraction of the value of the irrigated crop obtained. The benefits have been clear and important in most cases. In poor countries groundwater development has provided reliable drinking water supply and increased food security through irrigation, and consequently groundwater as become a relevant means of eradicating poverty. The impact of this groundwater development in developed countries is also significant but not yet well recognised. But sometimes, there are other associated negative effects. These sometimes have been utilised by certain lobbies to expand the hydro-myth of the unreliability (or fragility) of groundwater development, in order to continue to promote the construction of large hydraulic infrastructures. In Spain, groundwater irrigation accounts for more than 50% of the total economic value of irrigated agricultural production, while it only consumes about 20% of the total volume of water. In spite of its benefits, groundwater has not been a significant part of Spanish water policy.