 Countries must learn to share water fairly if they are to avoid warring over the vital resource as population growth and climate change make it ever more scarce, the head of the UN farming agency said on Thursday. Farming consumes 70 percent of the fresh water taken from the world's lakes, rivers and aquifers and demand from farms is set to increase by 14 percent in the next 30 years, said Jacques Diouf, head of the Food and Agriculture Organisation (FAO). "Water conflicts can arise in water stressed areas among local communities and between countries," he told a conference marking World Water Day. "The lack of adequate institutional and legal instruments for water sharing exacerbates already difficult conditions. In the absence of clear and well-established rules, chaos tends to dominate and power plays an excessive role," he said. While humans drink between two and five litres of water a day (0.4-1.1 imperial gallons), it takes 1,000-2,000 litres to produce a kilogram (2.2 lb) of wheat and up to 15,000 litres to produce a kilo of grain-fed beef, according to the FAO. "The effective daily consumption of water per person is a thousand times more than the apparent consumption through drinking," Diouf said. Already 1.1 billion people lack access to adequate clean water and, with the world's population set to grow from the current 6.5 billion to 8 billion by 2025, 1.8 billion people will face water scarcity by then, the FAO estimates. Global warming will exacerbate the problem, especially in poor, arid areas, Diouf said. To improve cross-border cooperation on water use, the 10 countries on the Nile are negotiating a water sharing agreement which the FAO hopes will be a model for other areas where the scarce resource can be shared out peacefully.