“Water, water, everywhere, / And all the boards did shrink; / Water, water, everywhere, / Nor any drop to drink”. Samuel Taylor Coleridge wrote these lines at the end of the eighteenth century, but they ring dramatically true for many countries in the world also in present days. Despite the planet is literally covered by salt water, only a tiny proportion (nearly 1%) is freshwater accessible for human purposes. Water scarcity, occurring when the requirements of all sectors cannot be met fully due to constraints related to water quantity or quality, currently affects about 40% of the world population. Future projections are not reassuring, as they predict that, in 10 years, 1.8 billion people will be living in areas suffering from absolute water scarcity and about 60% wi...