1. Introduction
According to the IEA (International Energy Agency), roughly 1.5
billion people around the world do not have access to electricity
[1,2]. Regarding water supply, the numbers provided by the WHO
(World Health Organization) are also alarming: 1.1 billion people do
not have access to any types of improved drinking source of water
[3] and around 50% of them have some health issues related to lack
of clean water sources and sanitation systems [4].