subsurface storage is achievable without loss of water-spread areas suitable for cultivation or other beneficial land uses;
groundwater can be put to use where and when it is required, with less risk of seepage or evaporation losses during storage and transmission;
there is less ecological hazard compared to surface storage projects;
groundwater storage is less liable to deterioration than surface storage;
the cost of storing groundwater is less than that of surface storage.
In spite of the many advantages mentioned above, there are some constraints that hinder groundwater storage, such as:
wells interfere adversely when large supplies are required;
groundwater storage withdrawal is a highly energy intensive process, while surface water is often available by gravity flow;
surface reservoirs are more suitable for multiple uses, including energy production and recreation;
mineralization is generally lower in surface water storage.
The current trend in aquifer management focuses on determining the maximum and minimum water levels, in order to regulate storage capacity. As a matter of fact, uncontrolled overexploitation causing progressive drawdown below the minimum permissible piezometric levels, will lead to increased pumping costs, land subsidence, infiltration of poor quality water, drying up of springs and shallow wells, decreased river flows. Moreover, in coastal aquifers the prolonged reduction of freshwater flow towards the sea reduces the equilibrium gradient, inducing saltwater intrusion and the inland movement of the freshwater – saltwater interface. Combining so many aspects requires methods of analysis that systematically integrate them in such a way that within