The drums of war are beating again in the Middle East and the Horn of Africa. But this confrontation doesn’t concern Syria, Somalia, Israel or the Palestinians. The adversaries are Egypt and Ethiopia. The flashpoint is the waters of the Nile.

As part of the construction of its Grand Renaissance Dam, Ethiopia began partially diverting the course of the Blue Nile, which joins the White Nile in Sudan before flowing on to Egypt, in late May. For Ethiopia, the 6,000-megawatt Grand Renaissance project -- the largest hydroelectric plant in Africa -- promises power for the 83 percent of the population lacking access to electricity, as well as energy for export.

For Egypt, though, the dam raises an existential alarm. Egypt receives almost no rainfall. It depends on the Nile for 97 percent of its renewable water resources. The Nile, in turn, depends on Ethiopia. More than four-fifths of the water in the river first falls as rain in the Ethiopian highlands.

Ethiopia maintains the Grand Renaissance project won’t harm its neighbors. But Egypt fears the mile-long, 560-foot-tall dam -- and the 74 billion cubic meter reservoir behind it -- could diminish the vital water supplies ultimately available downstream.

Despite the saber rattling rhetoric, there’s little chance Egypt and Ethiopia will actually cross swords over the Nile. Both countries have far too much to lose from war. Yet, while a clash of arms remains highly unlikely, the clashing demands on the Nile’s shared waters are real and symptomatic of similar conflicting claims over scarce water resources in other nations as well.

Around the world, growing population pressures, unsustainable consumption patterns and escalating environmental stresses are imposing mounting strains on freshwater resources.

From the Nile to the Tigris-Euphrates to the Indus, many of the Earth’s major river basins are increasingly considered “closed.” This means that all their available renewable water is already allocated to various human and environmental needs, with little or no spare capacity.

Some closed rivers, such as the Colorado in the U.S. and Yellow River in China, no longer always run to the sea. With scant buffers to absorb new demands or fluctuations in supply, water use changes in one part of the system readily reverberate to users elsewhere in the basin, squeezing consumers and policymakers alike.

More than 1.4 billion people now live in closed basins. If present trends continue, rising water demands for agriculture, industry and domestic needs will risk outrunning sustainable supplies in many more regions worldwide.

According to projections by the 2030 Water Resources Group -- a consortium led by the World Bank and the consulting firm McKinsey -- global water requirements will exceed renewable resources by 40 percent in 2030 if there aren't considerable efficiency gains and policy improvements. In China, available water supplies will fulfill just three-quarters of anticipated demand 17 years from now; in India, only half.

Global climate change will exacerbate these challenges. Shifting precipitation patterns threaten to reduce water availability in some regions while inflicting stronger storms on others, increasing both potential droughts and floods.

Meeting the world’s growing water needs will require far more effective use of available resources. An alarming amount of the water now drawn from rivers and lakes or pumped from underground aquifers is wasted. In many countries, for example, 40 percent or more of all the water withdrawn for agriculture is squandered, evaporating into the air or seeping into the ground from poorly maintained canals before ever reaching farmers’ fields. Many cities lose a similar proportion of their municipal water supplies to leaky pipes.

Ultimately, however, sustainable management of the world’s freshwater supplies will necessitate enhanced collaboration, between sectors and communities within nations, and between countries in international basins.

Shared water resources tie consumers inextricably together. Water policy choices made by one user can impact the timing, location and amount of water available to other users. Contrary to the martial rhetoric currently heard on the Nile, confrontation can't navigate these trade-offs and conflict can't help meet rising water demands. Only cooperation can.

On the Colorado River, for example, a creative new agreement between the U.S. and Mexico allows U.S. states to finance irrigation improvements in Mexico and then share in the additional water supply freed by the ensuing efficiencies.

Similar cooperative approaches could defuse tensions on the Nile. Funding the Grand Renaissance project currently exerts substantial pressure on the Ethiopian treasury, even as Ethiopia aims to export much of the resulting hydropower. A joint venture with downstream Egypt and Sudan to manage the project together could ease Egyptian anxieties, while facilitating financing for the dam and securing partners and markets for expanding the regional power grid.

Unlike policymakers, water resources ignore political boundaries. Water managers must learn to manage the world’s shared water supplies as allies rather than adversaries, or we will all suffer the consequences of increasing water shortages.

David Michel is director of the Environmental Security Program at the Stimson Center, a nonprofit and nonpartisan think tank that studies peace and security challenges around the world.