"I've already earmarked a customer for this drum -- I need to get a move on!"
Ali Ahmat,12, flicks his whip to persuade a hard-driven horse to press on with his cart, laden with 200 litres (44 imperial gallons) of freshly-fetched water.
The young entrepreneur is one of the informal but indispensable links in a chain to supply people in Ouaddai, eastern Chad, with water, the stuff of life.
Scorching temperatures, an open sky, a shortage of deep wells and lack of water purification system make this a thirsty part of the world indeed.
"After the rainy season, water becomes scarce," says Mahamat Adoum Doutoum, chief of the Guerri region, where only two deep wells exist for 86,000 inhabitants. "So people go to look for water in the wadi."
Wadis -- "riverbeds" in Arabic -- are watercourses that run strong and fast during the rains and are often dangerous to cross, but largely dry up for the rest of the year. When there is no more rain, people dig wells in the wadis and install pumps to extract groundwater.
Ali and dozens of other water carriers flock to the pumps to collect supplies they plan to sell to people who have no access to the source, often in dusty settlements.
Each refill of his 200-litre drum costs Ali 100 CFA francs (0.15 euros / $0.17), but he can sell the water for five times as much in town. "We do between seven or eight return trips each day, roughly," he says.
Towards the end of a hot Sunday, the blazing sun has set and Ali's cart is heading towards Hadjer Hadid.
The town harbours a refugee camp for people who fled conflict and mass killings in the Darfur region of western Sudan, the far side of the border.
Pascal, a Sudanese refugee and father of five in his 50s, is also used to the return trips between the town, the bed of the wadi and the muddy wells.
He first came to Chad about 15 years ago and says that he "suffered" to be able to buy his own donkey.
The beast of burden was an investment that has paid off, however, enabling Pascal to deliver water to the townsfolk over the past two years and bring a small sum home to his family.
But he remains concerned about the quality of the water.
"To drink the water, you also have to add bleach," Pascal says.
While water has become as rare as it is valuable, the kind to be found around wadis is unsafe. Traditional wells dug into the earth at the wadis provide water that is often the same colour as the soil.
"The water can be contaminated at various points, either at the source, which may be unprotected, or during transport, using receptacles which are inappropriate, dirty or uncovered, and during storage and distribution," says Fabienne Mially, mission chief in Chad for the French aid group Premiere Urgence Internationale (PUI).
The NGO supports 11 health centres in the Ouaddai region, where awareness sessions on the importance of proper drinking water are regularly organised.
In Borota, a village several hours' drive from Hadjer Hadid, the head of the local health centre has no illusions. Of the six standpipes in the village, none is working any more.
"They were installed by NGOs," says the official, Koditog Bokassa, who says that wadi water is the only available source of water locally.
He hands out sachets of bleach to dilute in untreated water.
But Bokassa lacks the means to satisfy everybody and PUI has become the sole supplier of bleach in central parts.
The state used to deliver some, but has not done so for more than a year, he says. It is quite common to see young people at the wadis drink directly from their cans.
The town has holding basins and water towers designed to retain water during the rainy season.
"But the holding basins are insufficient and the two water towers broke down several years ago," says local resident Hassan.
One trader has bought two barrels of 200 litres apiece, which he leaves in the courtyard of his house. "It's barely enough for the children, but it's better than nothing."
The water deliverer Pascal does not have the money to buy a drum of such munificence. For the seven members of his household, there are seven 20-litre cans on the stoop.
"I haul water every day, but I have the same problem as everyone else," he said.