ABSTRACT
Groundwater constitutes the largest reservoir of freshwater in the world, accounting for over 97% of all freshwaters available on earth (excluding glaciers and ice caps). The remaining 3% is composed mainly of surface water (lakes, rivers, wetlands) and soil moisture. Until recently, focus on groundwater mainly concerned its use as drinking water (e.g. about 75% of European Union (EU) residents depend on groundwater for their water supply), while recognizing that it is also an important resource for industry (e.g. cooling waters) and agriculture (irrigation). It has, however, become increasingly obvious that groundwater should not only be viewed as a water supply reservoir, but should also be protected for its environmental value. Groundwater plays an essential role in the hydrological cycle and is critical for maintaining wetlands and river flows, acting as a buffer during dry periods. In other words, it provides the base flow (i.e. the water which feeds rivers) to surface water systems, many of which are used for water supply (including irrigation), energy production, recreation etc. In many rivers across Europe, more than 50% of the annual flow is derived from groundwater. In low-flow periods this figure can rise to more than 90% and hence, deterioration of groundwater quality may directly affect related surface water and terrestrial ecosystems.
