The hydrological cycle and the mythical conception of water The water cycle comprises four parts: a. The sea b. To a minimum extent, the vegetation cover c. Atmospheric water: water vapor and clouds (transfer, condensation, precipitation) d. The superficial continental water (rivers, lakes) and subterranean water that ends up returning to the sea after a more or less long time, except for the fossil waters. For millennia, humanity has considered water as a non-modifiable element of the globe, like air; and in antiquity, in an essentially rural world, water was greatly disconnected from economic circuits since the source, the river, the well and the cistern fed the populations without any cost or very low, depending on the servile condition or not of the workforce. Water was a gift from the gods. The aversion to modify the cycle of nature is evident even in the ancient Romans and city dwellers in particular. So they turned the mills night and day and fed giant fountains and hot springs. The nautical games needed the creation of specific circuses, the naumaquias. The historian Pierre Grimal calls Rome "the city of water", since eleven important aqueducts fed the city at the end of the empire. But, already to the 144 before J.C., the technique of the inverted siphons was dominated thanks to the use of conduits of lead, abundant metal in present-day Spain. According to bibliographical sources, the available water transported per inhabitant reached in Rome approximately 1000liters/ day under the rule of Trajan (98-117 after J.C.). But this evaluation does not take into account huge leaks and losses of the old network. Fall Rome, then Constantinople, the taste for the fountains, for the water games and the hot springs is perpetuated and perfected in the Arab and Persian world, before penetrating again in Europe in the Baroque period. However, the fashion of thermalism only really took place in the eighteenth century and especially in the nineteenth century, with the rediscovery of the body and the cult of hygiene. Marienbad, Vichy, Baden-Baden, Spa, Bath and Montecatini flourished. In France, the Empress Eugenia promoted by her example the spas. Guy de Maupassant realistically describes in "Mont-Oriol" (1887), the birth of a thermal city in the countryside. 3,4 Water was a gift from the gods as the source tree or holy tree of the Canary Islands, which captured water from the mist until 1610 and fed the pre-Columbian populations of the island of Hierro. 5 For the Incas, Lake Titicaca was the center of the original world. In Aztec Mexico, Tlaloc was the god of rain. Symbolized by a frog or a frog, it was the divinity of the peasants. In fact, water was the essential factor in the stability and organization of the pre-Columbian peoples of Mexico. Finally, in the new world, around 1730, the coming of rain was still a divine phenomenon for Bartolomeo Arzáns, chronicler of Potosí, the largest American city of the seventeenth century. 6 Water as a danger and source of conflict One of the sources of danger and conflicts of wat...