The Canary Islands represent an almost perfect model of reference in the field of the water desalination. Starting from the 1960s, many desalination plants have been built to provide fresh water from non-conventional sources; making it necessary to search from other sources of supply, like seawater or brackish groundwater. Desalination in the Canary Islands has contributed to the progress and development of the islands, considering that its main economic activity is the tourism. In addition, water desalination has improved the population life quality, allowing a safe and continuous supply of water for domestic and agricultural consumption. Nevertheless, the desalination systems show a high power demand with a strong dependency on the non-renewable energies, basically of oil products. The desalination technologies that require electricity have gradually reduced their energy consumption, lowering the water supply bill. The reduction has been made possible thanks to the development and consolidation of efficient methods or through improvements in the equipment of desalination itself. In the present paper, we analyse with a retrospective vision the evolution experienced by the consumption of energy in the existing desalination plants in the Canary Islands, as well as the outlook in the long term. We will try to answer questions that we are considering nowadays, as it is for example whether the industry has arrived at the bottom line in energy consumption, what is the optimal size of a plant and its energy consumption of energy, etc. In our discussion we will consider the conditions of design and operation, as well as the different technological changes that have occurred during the life time of the installations. This exposition will allow us to learn in depth the existing deviations in the energy consumption and therefore, to include or understand the solutions adopted. The final objective is to contribute by explaining the state-of-the-art on the existing relationship between the energy consumption and the water desalination, by means of the knowledge of the improvements and decisions taken at each moment in a part of the world, where the water desalination accumulates more than forty years of experience.