For centuries, it has been considered freshwater as an inexhaustible resource and has been mismanaged. Throughout this century has fresh water becoming increasingly scarce. In some parts of the world (as in Africa) has been producing a gradual desertification mainly affecting poor countries. Many of them have large areas of arid desert coast and have at their disposal large amounts of water, the sea, with the disadvantage of being salt and therefore unfit for human consumption. In industrialized countries without problems - in theory - of water began to see, from the 60's, the need to regulate water resources: spending, recycling and distribution of water, as water demands and supply problems were increasing with increasing population, living standards and industrialization. Polluted rivers and streams with increasingly low and depletion of water reservoirs has led to the gradual increase in the salinity of inland seas and estuaries and seawater infiltration at sites close to the coasts. Water consumption worldwide has increased by 7 during this century. Currently the average water consumption is 1.2 m3/day per capita and water scarcity is considered a consumption less than 1,000 m3/year per capita. Currently there are 26 countries, representing about 430 million people, who do not possess the minimum water supply and it is estimated that these figures can be multiplied by four over the next 50 years.