A scramble for cheap African farmland by foreign investors threatens to leave millions of people without water and could ultimately drain the continent's rivers, a report warns.
"If these land grabs are allowed to continue, Africa is heading for a hydrological suicide," said the report's co-author Henk Hobbelink, coordinator of GRAIN, an organisation supporting small farmers.
Foreign governments and wealthy individuals are snapping up millions of hectares of land on the continent for large-scale agriculture projects to grow food and biofuels for export.
But the report warns there is simply not enough water in Africa's rivers and water tables to irrigate all the newly acquired land.
In some cases communities are already being moved off land to make way for these mega-projects. In others, the plantations will divert water from rivers that local people depend on for their own farming and everyday needs.
"Millions of Africans are in danger of losing access to the water sources they rely on for their livelihoods and for the survival of their communities," Hobbelink said.
"The worst case scenario is indeed we end up with a situation where the entire continent's river systems will dry out."
Hobbelink said the land deals - many of them along the Nile and Niger rivers - were already creating tensions in some parts and could fuel conflict.
Countries leasing land include Sudan, South Sudan, Ethiopia, Egypt, Zambia, Kenya Tanzania, Mali and Senegal.
The report, Squeezing Africa dry: behind every land grab is a water grab, said those acquiring farmland knew that the access to water they were automatically gaining - often without restriction - could well be worth more in the long term than the land deals themselves.
Agriculture already sucks up around 70 percent of freshwater used globally. But demand is likely to soar as the world population increases.
Investors come from India, Saudi Arabia, China, UAE, Libya, Qatar, the United States, Britain, France and Canada among others, according to GRAIN.
But the report said Africa was in no position to support these massive new agribusiness projects - one in three Africans already lives with water scarcity and climate change will make things worse.
Hobbelink also pointed out that in many parts of Africa there were distinct dry and rainy seasons and local communities had adapted their farming methods to suit these fluctuations. But he said many crops being farmed on the new plantations, including rice, sugar cane and palm oil, required huge amounts of water all year round.
Much investor interest is focused on countries in the Nile basin. The United Nations' Food and Agriculture Organisation (FAO) has estimated the ten countries in the basin have enough water to irrigate a maximum of 8 million hectares.
But four countries alone - Sudan, South Sudan, Ethiopia and Egypt - have already established irrigation infrastructure for 5.4 million hectares and leased out a further 8.6 million hectares.
Tensions have already flared over one project in Gambela in Ethiopia. The plantation, owned by Saudi-based billionaire Mohammed Al-Amoudi, is irrigated by water diverted from the Alwero River which locals depend on for fishing and farming.
In April an armed group ambushed Al-Amoudi's Saudi Star development operations, leaving five people dead, according to GRAIN's report.
Advocates of land deals and irrigation projects say these big investments in Africa should be hailed as an opportunity to tackle hunger and poverty. But Hobbelink said people were being paid as little as 70 cents a day to work on projects.
"Virtually all the land use we've seen is about installing huge plantations and removing people from their territories," he added.
"It's more about creating poverty than helping to address it."
Hobbelink said the key to ending poverty was to invest in and improve on local technologies and methods for managing and conserving water.
"We think the current drive for land-grabbing, as we call it - which is what we think it is, has to be stopped," he added.
GRAIN's report comes ahead of the Rio+20 summit on sustainable development. Water will be one of the key topics under discussion when the meeting opens on June 20.