A dispute is growing between Ethiopia and Egypt over access to the waters of the Nile.
Ethiopia believes it could irrigate parched lands with Nile water
Ethiopia, the source of the Blue Nile, wants to take more water from it - claiming it could wean itself off food aid if it could irrigate from the river.
However, a 1929 agreement between Egypt and Britain - the regional power at that time - gives Egypt most of the Nile's water, and Egypt has said it cannot afford to give up this claim because of the needs of its own booming population.
"We generate about 85% of the total Nile waters - we have not utilised this resource at all so far," Misfinta Genny, Ethiopia's deputy minister of water, told the BBC World Service's Assignment programme.
"The amount we use so far is next to zero. So we must develop these resources, basically for the benefit of our people."
The waters of the Nile have for years preserved life and agriculture for the people of east Africa. The lack of rainfall in the region means that some countries rely almost entirely on the river for their annual supply.
But now rising populations, and the spread of the Sahara desert, have placed extra strain on what is available - increasing political tensions across the region.
Constantly failing rains in Ethiopia have made it impossible to grow virtually any crops, and Ethiopia's Ministry of Water Resources has grown increasingly frustrated by its inability to make use of the Nile's water.
Cairo's intense population density means Egypt needs new towns
It is estimated that irrigation schemes would help 30-40% of the population - around 15 to 20 million people.
But there have now been claims that Egypt is blocking donations from developed countries to Ethiopia to develop large-scale irrigation.
Some Ethiopians believe that because Egypt is almost totally dependent on the Nile's water, it is doing its best to block any large upstream irrigation project that might threaten its supply.
And Egypt is reported to have said it would regard any attempt to alter the Nile status as an act of war.
The pressures on the river's waters are increasing in Egypt, too.
"It's not only for production of food - it is also for generation of employment," explained Dr Dia al Qazay, a senior adviser to country's Ministry of Water Resources and Irrigation.
"Forty percent of our manpower is farmers. If these people are not given opportunities and jobs, they'll immediately move to the cities and urban centres. And you can see already how crowded Cairo is."
Dr al Qazay pointed out that Egyptians live on only 5% of the country's land, as the other 95% is desert.
"We want to relieve these major cities and urban centres from this heavy population density," he added.
As a result, one aspect of government policy has been to create new towns, linked to the Nile by canals, such as Nubia in the north - created entirely from scratch in 1987.
But creating new towns in the middle of the desert consumes large volumes of water.
Egypt's population has more than doubled since the 1960s, and is continuing to soar, putting an ever-increasing strain on the Nile.
Water war worries
Among those worried by the demands on the Nile is Dr Boutros Boutros Ghali, the former secretary-general of the United Nations.
Dr Boutros Ghali says a booming population needs more agricultural land to feed itself - and that countries belonging to the Nile basin need at least the same quantity of water.
"This is why the security of Egypt is related to the relationship between Egypt and Sudan, Ethiopia, Kenya and other African countries," he explained.
Boutros Boutros Ghali has warned of "water wars" for over 20 years
Dr Boutros Ghali accepts that satisfying Egypt's needs will mean less for these countries - which also have fast-growing populations, and want more water for large-scale irrigation themselves.
"Now, we have a real problem... we need an additional quantity of water, and we will not be able to have this additional quantity of water unless we find an agreement with the different upstream countries - which also need water, and have not used the Nile water until now," he added.
And he warned that a lack of agreement in the future would "certainly" result in "military confrontation between countries in the region".
"The next war among countries will not be for oil or territorial borders, but only for the problem of water," he said.