ACQUA E SOCIETA' UMANA. IL CICLO DELL'ACQUA: DISPONIBILITA' E IMPIEGHI

In recent years water has become an increasingly important resource, not only because of the increase in applications connected with it but also because it is an important indicator of the improvement of the quality of life. Consequently only a proper understanding of the water cycle, and in particular of the distribution and availability of water resources over space and time and the imperatives arising from man-made change, will enable us to evaluate their sustainability and manage them properly with a view to the sustainable development of human activities. It is not easy in practice to gather the data that allow us to quantify these things, above all so far as resource use is concerned, since what we have is not measurements (from meters, for instance) but abstraction permits - which represent potential demand. It is easier to work out (approximately, at least) the availability of resources than their use; and it is accordingly impossible to establish the water balance. However that may be, it is clear that water use far exceeds availability, and accordingly that water management is hard to make sustainable: we face a situation of grave water shortage. All the same, we need to consider the following: the use of water for hydroelectric power generation is not actually consumption (since the water is returned further downstream), but only a local reduction of the river's flow, though this may pose problems in terms of maintaining the vital minimum flow; irrigation water is consumed (for farm production), but part of it (30-50%) soaks into groundwater or returns to watercourses; water's quality deteriorates after use, and it cannot therefore be reused in the public supply without adequate treatment. The consumption of water by human activities has increased immeasurably over the last hundred years. According to a UNESCO report (Zektser, Everett, 2004) total consumption of water in Europe was 40bn m3 in 1900 and 720bn m3 in 2000, and the breakdown by type of use was also very different, domestic and civil use rising from 9bn m3 to 77bn m3, industrial use from 9bn m3 to 320bn m3 and agricultural use from 23bn m3 to 320bn m3: consumption increased almost twenty-fold, while the availability of water from precipitation did not change significantly in the same period. The emergence of water shortages and their critical nature are not therefore so much a matter of diminishing supply, but of a disproportionate increase in the use of water resources. Changes in precipitation related to climate change involve on the one hand a reduction in precipitation which is small in percentage terms but mainly concentrated in particular periods of the year and can be important for agricultural production, and on the other hand a rise in temperatures, which in turn causes greater use of water resources. The problem is not, therefore, one of finding more water but of consuming less - of making more rational use of what is available. It would be insanely short-sighted to use stored water - stored groundwater especially - because that is a strategic resource for dealing with normal needs in abnormal circumstances. We shall be able to overcome these problems only through greater awareness of the issues surrounding water; and this could arise from better public knowledge following duly disseminated explanations of the processes affecting water, and in particular of the Water Cycle. Rising world population, understanding of the limited availability and sometimes inadequacy of water resources, each country's imperative need of reliable water supplies year in year out for its development, widespread desertification and increasingly frequent droughts (and floods) have all combined in recent years to raise water's profile and make us pay more attention to th