Another important constraint on the optimal use of water resources, when two or more countries share a hydrologic system, is politics.

This is the situation that led to the far too often repeated 1991 remark of Ismail Serageldin, at that time a Vice-President of the World Bank, to the effect that "The wars of the next century will be about water !" .

There are indeed several well-known places where competition for water has led to high inter-country political tensions. Bangladesh has complained for decades about the small fraction of the Ganges that is prevented by India from flowing downstream from the Farakka Barrage. Egypt is deeply concerned that water development in Ethiopia or the Sudan could threaten its tightly stretched share of the Nile. Jordan has for year tried to negotiate a peaceful sharing of the waters of the Jordan basin with Syria and Israel.

• There are many more situations like this on the list, but the facts are that there are many other excuses for war, when war is wanted for other political or economic reasons, e.g. oil, and;
• most of the pairs of countries that are in this situation are so unequal in military strength that the weaker of the two could simply not afford to 'go to war' over the water (or any other) issue.