In the future, something else will start taking over from oil as the likeliest cause of conflict. It's an ever scarcer and more valuable commodity: WATER. The fear is that as populations grow and development spreads, vicious battles will erupt between water-rich and water-poor nations, particularly in major river basins where upstream nations control the flow downstream water.

The doomsayers warn that global warming will only make things worse by decreasing rainfall and increasing evaporation in critical areas. Our future will involve scarcity of water, though forecasts of vast deserts are a little too exaggerated.

Many of the arguments that have been applied to Peak Oil are also applicable to water. If the current rates of growth in supply and demand continue, then water will become a very scarce resource. When I was in India recently, there was a BIG strike between neighboring states over new laws that changed water rights. As water becomes more and more scarce in populated areas, conflict will inevitably be the appropriate response to water shortages.

Are we heading for an era in which rivers and lakes and aquifers become national security assets that are fought over? With water availability shrinking across the Middle East, Asia and sub-Saharan Africa, violent conflict between states is increasingly likely. Major government agencies, including the CIA, have already raised the specter of future "water wars".

Said Mark Twain, "Whisky is for drinking, water is for fighting over". In August 2007, experts from 140 countries will gather at the annual World Water Week forum in Stockholm. And the ghost of Mark Twain will be present as they debate the links between water scarcity and violent conflict.

• World Water
• Wars for Water