The purpose of this lecture is to raise youngsters' awareness about the importance of water for the survival of human beings and living creatures. It is worth noting that Tunisia, because of its geographical location, is under the influence of two climates, the first one Mediterranean in the Northern part, the second one Saharan in the Southern part, both causing invariability in rainfall and thus in water resources. The average rainwater at the deep South is about 100mm a year, while it varies between 200mm to 400mm a year at the centre and reaches 1500 a year in the Northern part of the country.