Freshwater has two other important characteristics that we have to reckon with. On average, the water in rivers is replenished every 18-20 days, but a single molecule of water may take up to a year to complete the whole water cycle. The other significant feature of the water resource is that it is unevenly distributed. Of the 129 cubic kilometres of freshwater available on the planet, South and Central America are endowed with 43 of them, Asia 36, North America 22, Africa 21, Europe six, and Australia only one. Within the continents, particularly in Africa and Australia, the distribution is also very uneven.
Water is critically scarce in many places.
In general, it is considered that a country will experience periodic water stress when the supply goes below 1700 m3 per person. On average, the planet has some 7400m3 of water per person, but there are 22 countries that have less than 1000 m3 per capita, and 18 more countries with less than 2000 per capita. The scarcity of water has placed the issue at the top of the international political agenda. Thus, managing water with a sound whole-basin approach requires a strong dose of political will to cooperate for the common good. Otherwise, water, the source of life, could easily become the source of deadly confrontations.