Global water demand is continuously increasing with an expected rise of the 20–30% for 2050 that is mainly attributable to the strong link of water use to population growth and socio-economic development (1). Also, drought episodes are expected to be more frequent, severe, and last longer in many regions of the world as an effect of global warming and climate change.
In Europe, drought events are becoming an even more important problem, and not only in the Mediterranean basin, which is traditionally used to suffer them periodically. This year, it has been the third consecutive one of severely dry conditions, and during Spring, central and northwestern European countries, which are not traditionally dry ones, such as Germany, Belgium, the Netherlands, Ireland, and most of the UK had experienced warmer temperatures and poor rainfall, which have reduced, for example, crop yield in central and eastern Europe (2).
Therefore, it is necessary to look for alternative water sources to reduce the dependency on direct rainfall to store water recharging aquifers, which are natural reservoirs to alleviate the effects of drought episodes. In fact, a 75% of the inhabitants of the European Union depend on groundwater for drinking water supply (3).
Water reclamation from industrial and urban wastewater, treatment plants, and water regeneration from rainfall, promotes increasing water availability for different uses. Nowadays, it is possible to treat wastewater to meet the most exigent quality demands, such as drinking use. One remarkable example of this is in Singapore, where the plants of the NEWater initiative, supply up to 40% of Singapore's current water needs for different uses, including drinking water (4).
A similar approach occurs in California, where recycled water includes; conservation, capture, and use of storm-water, aquifer storage, and other strategies, such as wastewater reclamation, which enables a more sustainable and reliable long-term water supply in this state (5).
Other examples in Spain, are “El Pinedo” wastewater plant in Valencia, where every year reclaimed up to 78 hm3 of water for crop irrigation use, alongside the environmental restoration of “La Albufera” natural park (6); and the wastewater treatment plant of “Arroyo Culebro” in Madrid, whose water reclamation initiative, supplies reclaimed water to a paper mill, enabling to completely replace the use of natural freshwater resources for industrial production (7).