In her Essay 'Do nations go to war over water?' (Nature 458, 282–283; 2009), Wendy Barnaby quotes from my 1995 speech in Stockholm, in which I said “The wars of this century have been on oil, and the wars of the next century will be on water ... unless we change the way we manage water”. The opening part was picked up by the media as a sound bite that was nevertheless valuable in pushing water issues up towards the top of the agenda, although the caveat, the operative part, was largely overlooked.

However, I do not consider that to be alarmist. I know all the arguments that have been made by others about international wars being unlikely for water, and they are probably right. But civil strife between competing groups within countries over water rights are very serious. Many of the wars of the past 20 years, on issues other than water, have been between groups within one sovereign state. That did not make them any less murderous.

Furthermore, the century is just starting and we have not seen the full range of expected environmental, demographic and political challenges unfold. Water in this century will become a major source of strife between groups within countries. Drought has driven many tribes in Africa into terrain that they are not normally expected to occupy. When coupled with other factors such as ethnic or religious divides, this becomes a dangerous mix.

Water may also become a casus belli between states, if the downstream nation is considerably stronger militarily than the one upstream, and the latter tries to block or reduce the flow of water. Whether it is acted on or not depends on many other issues, including the nature of the relationships between the countries concerned.

Solutions will require actions on many fronts, including in many other sectors with which water interacts economically and environmentally. But much also remains to be done to improve our resource management in the water sector broadly defined: water for food, industry, energy, domestic and municipal use, and for the environment.

The answer to the clarion call of 1995 to avoid 'water wars' is to manage our water resources better, learning from past experience, generalizing best practices and facing up to the mounting challenges that are coming our way, not to dismiss the issue as a myth.

See also: Water: resistance on the route towards a fair share for all The potential for water conflict is on the increase Increasing inequality is already making shortages worse Water is a source of cooperation rather than war