Two types of tankers compete for space on the roads lined with shacks that lead to the docks in Luanda, the Angolan capital: water and oil. More than half the people living in informal settlements, called musseques, depend on private tankers for their daily water in the oil-rich country.

More than 300 privately-owned trucks bring water into the city every day from a pumping station in Kifangondo, 20km outside Luanda on the Bengo River, and the pumping station is run by the National Association of Truck Water Distributors.

The public-sector water company in Luanda, EPAL (Empresa Publica de Aguas de Luanda), was hobbled by almost three decades of conflict that ended in 2002, and has not recovered.

During the war, thousands of people fled conflict in the countryside to seek refuge in the capital, which was built to accommodate around 400,000 but now has about 4.5 million residents, according to the UN. EPAL could never have kept up with the exploding demand.

"Despite impressive revenues from oil and diamonds, there has been virtually no investment in basic services since the 1970s, and only a privileged minority of the people living in Luanda have access to running water," said a briefing paper by the international medical charity, Médecins Sans Frontières (MSF), called 'Murky Waters: Why the cholera epidemic in Luanda was a disaster waiting to happen'.

"The rest of the population get most of their water from a huge network of water trucks that collect water from two main points [Kifangondo on the Bengo River, and Kikuxi on the Kuanza River, both outside Luanda] and then distribute it all over town at a considerable profit," MSF's paper commented.

At dawn, the water tankers make their way down the narrow, dusty, dilapidated road to Kifangondo. On most days, the drivers take at least an hour to travel the 20km stretch, while the queue for water builds up in the musseques.

Miguel Domingo, chair of the water distributors' association, said the private sector geared itself up 20 years ago, during the war, because it realised the business potential in providing an essential resource like water. It set up pumps and installed pipes big enough to fill around 450 tankers per day, about five million litres, according to the MSF paper.

Raw water is pumped from the River Bengo into the waiting tankers, which then go to a chlorination point, where the drivers buy a container of chlorine and pour into the water before leaving the pumping station.

In 2006, when Luanda was going through its worst ever cholera epidemic, with an average of 500 new cases per day, MSF found that many trucks were leaving the station without chlorinating the water, to avoid queuing and make as many round trips as possible.

Cholera

But the 2006 cholera outbreak in Angola in which 67,257 cases were recorded and 2,722 people died - the world's highest fatality rate - shook the authorities.

Since then, a policeman and a water affairs official have been stationed at Kifangondo to ensure that no truck leaves with raw water, according to Maria Trajo, the Chief of Water Quality at the government's National Directorate of Water.

But aid agencies do not rule out the possibility that some tankers are still selling untreated water. "Truck drivers can be in a rush and do not want to queue to buy the chlorine," said an aid worker who wanted to remain anonymous.

The trucks usually sell to water vendors, who then sell by the bucket to householders. "The chances of the water getting contaminated are very high," said Allan Cain, director of the Development Workshop (DW), an anti-poverty non-governmental organisation.

"We don't know [the vendors'] underground water tanks are regularly cleaned; besides, each time a bucket is dipped into the water tank to be filled, the water is being exposed to the risk of being contaminated."

DW found that people living in the musseques were paying private sellers up to 10,000 times more for water than those who were better off and living in the part of city with piped water were paying the provincial water company for treated water.

MSF noted in its paper that the cost of water was determined by market forces. "Water prices are ... subject to speculation and can vary, even on a daily basis, depending on access (distance from the water collection point to the distribution point, and the condition of the road that leads to the final distribution point) and demand (availability of water in nearby areas)".

"It is a business worth several million dollars a year," said Dauda Wurie, the Water and Sanitation Project Officer of the UN Children's Agency (UNICEF) in Angola.

A family of four in the musseques, earning less than $50 a month, could spend as much as $60 on their monthly water needs. According to Cain, "this often does not include the basic minimum required per person per day - you might find families managing with a 20-litre jerry-can per day".

Domingo, of the distributors' association, denied allegations of profiteering and said they were willing to allow EPAL to take over the pumping operation, provided the public-sector company had the capacity to manage and maintain the station.

Pierre-Marie Achy, UNICEF's cholera coordinator in Angola, said the only safe solution was piped water for the entire population. Trajo said her department in the directorate of water had plans to provide running water to at least half the city's population by the end of 2008.