Categories, Distribution, Opportunities, and Challenges of Unconventional Water Resources

The water resources availability worldwide evidences the presence of many geographic areas characterized by water scarcity, an increasing generalized water demand due to population increase and a growth of anthropic activities water demanding. At the same time, climate change exacerbates weather extreme events, making water availability less regular, while diffuse pollution threatens water quality. In such a context, correct management of water resources becomes crucial, with the role of so-called unconventional resources growing and showing a relevant potential to integrate traditional freshwater resources with a relevant complementary quali/quantitative contribution. In the present Chapter, twelve different types of unconventional water resources have been presented and discussed in detail presenting their main features, potential, and limitations. They have been grouped into four categories on the basis of a similar ‘origin’, as follows: (i) Atmospheric Unconventional Water (AUW) resources, including fog water, dew water, cloud-seeded water, and rainwater; (ii) Processed Unconventional Water (PUW) resources, including desalinated water, wastewater treated, greywater treated, and agricultural drainage water; (iii) Transferred Unconventional Water (TUW) resources, including iceberg towed water and virtual water; (iv) Unconventional Ground Water (UGW) including artificial recharge and fossil water. At the present time a worldwide reliable distribution map of this unconventional water resources is not affordable, even if at regional level many data and information can be retrieved in the literature (including the grey one). Hopefully, also thanks to the growing use of artificial intelligence and machine learning, it will be achievable to build multi-component models, starting from the collection and classification of available data, to support decision makers. This will be of paramount relevance for optimal planning of water resource management, in order to adapt to and mitigate water scarcity and the effect of climate change, which is closely linked to it.