For years, Claude Surena has treated the sick at his two-storey hillside home near the centre of the Haitian capital. But the magnitude-7.0 earthquake brought the 59-year-old paediatrician's involvement to a whole new level.

Claude Surena has converted his property into a field hospital for more than 100 quake victims. His patients are treated in the shaded, leafy patio of his undamaged home while thousands of others in the city lie in the dirt under a merciless sun waiting for attention from a handful of doctors.

"I have to thank whoever brought me," said Steve Julien, who says the last thing he remembers before he blacked out was rescue workers calling his name as they dug through the rubble of his house.

It wasn't long after Tuesday's earthquake leveled nearly all of the houses next to Surena's that neighbors started showing up at his doorstep.

"It was a blessing from God my house is safe," he said. "We at least have been able to do something for everyone."

Surena has been relying on food and supplies salvaged from ruined homes to treat patients' broken bones and, for the dying, provide at least a minimum level of comfort away from the devastation.

The patients show physical and emotional wounds from having their homes collapse on them. Julien (48) is among the least severely injured, with only a few scrapes and a sore body. Others have compound fractures and festering wounds. Surena said at least 10 patients are in critical need of more substantial help.

The injured sing Christian hymns as they huddle close together beneath sheets strung up as tents, but the earthquake still haunts them. Aftershocks rattled the city as recently as Friday morning.

"Sometimes they just start crying. We still get some movement," said Surena, who is also the local district chairman for Haiti's disaster relief agency.

Meanwhile, hundreds of thousands of Haitians are in desperate need of drinking water because of the earthquake-damaged municipal pipeline and truck drivers either unable or unwilling to deliver their cargo.

"Many drivers are afraid of being attacked if they go out, some drivers are still missing in the disaster and others are out there searching for missing relatives," said Dudu Jean, a 30-year-old driver who was attacked on Friday when he drove into the capital's sprawling Cite Soleil slum.

The lack of water has become one of the greatest dangers facing Haitians in part because earthquake survivors stay outdoors all day in the heat out of fear of aftershocks and unstable buildings. While aid has started to pour in from around the world, supplies are not quickly reaching all who need them.

Even before Tuesday's quake, the municipal system in this city of three million people was unreliable. Haiti's poorest live in shacks with no plumbing and carry their water home in jugs from public wells. Most people depend on water delivered by truckers, who get their water with the help of diesel pumps that draw from a huge underground natural reservoir.

"There's no shortage of water – the water's here, the trucks are here as you see," said Jean, who said his attackers let him go unharmed after they recognised him.

Since the quake, at least one water treatment plant was shuttered because of a lack of electricity. Pipes for the municipal water system are believed damaged. No water is running in Cite Soleil, home to more than a million people. Adding to the problem is that stores that have water and food to sell are not opening out of fear of violence.

Tom Osbeck, a missionary from the US, said a scarcity of drinking water and food is fraying the nerves of increasingly despairing survivors.