Groundwater is an essential resource from a global perspective and provides the largest store of freshwater, apart from the ice caps. Current groundwater abstraction represents approximately 26 % of total freshwater withdrawal globally. Groundwater supplies almost half of all drinking water in the world and 43 % of the global consumptive use in irrigation. It is also important for industry and as an energy source. In arid and semiarid regions of the world, groundwater is the only reliable water resource. In the environment, groundwater makes an important contribution to baseflow in rivers and support groundwater dependent ecosystems.
For drinking water supply, one of the advantages of groundwater is that it is naturally protected from many contaminants. For example, suitable conditions of soil, climate, structure of the aquifer and groundwater flow can favour denitrification, naturally attenuating high concentrations of nitrates and other contaminants of anthropogenic origin. During droughts and with climate change, people in water-scarce areas will increasingly depend on groundwater, because of its buffer capacity and resilience to rapid impacts. However, groundwater quality, as well as quantity, may be impacted by climate change, which needs to be taken into account in groundwater assessments.
There are many reasons why a global groundwater quality assessment is needed:
- Human activities and climate variability are increasing the pressure on groundwater resources, but groundwater is an invisible resource that remains out of sight and out of mind for most people.
- Protection of our groundwater resources is necessary for protecting human health, maintaining food supplies and conserving ecosystems.
- Some regions and countries rely on naturally clean groundwater as advanced water treatment is economically infeasible. Knowing where to source clean groundwater, as well as understanding threats to this resource, is therefore important.