References
  -  C. Sommariva, Sustainability – A way to abundance, CRC
    Press, Taylor and Francis ISBN 9780815361688, 2018, chap. 5,
    pp. 94, 95. 
-  ADWEC Statistical Record 1999–2015, Electricity Statistics, pp.
    25,26. 
-  C. Sommariva, The evolution of the water sector 30 October,
    2016 https://www.meed.com/sectors/water/the-evolution-of-the-water-sector/5008974.arti. 
-  Dirk Uwe Sauer Technologien, Einsatzszenarien und Kosten
    von Speichern für elektrische Energie RWTH Aachen. 
-  Evolution scenarios for the water sector in the GCC: innovation
    and reorganization of the sector, IDA San Paulo 2017 conference
	  proceedings.