The family uses the water to cook, to wash and to drink, not because they want to, but because there is no alternative. Since moving about a year ago to the community of Virgen de la Merced on the western edge of the Amazonian rainforest, Rita has been suffering acute skin problems - irritation, redness and regular eruptions of boils and abscesses. She walks uncertainly, has difficulty breathing and is severely limited in how much she can do to help raise the animals and perform the daily chores.

Her mother goes through the painful ritual of washing clothes on a bare plank of wood in the garden, and hanging them up to dry on the strips of corrugated iron that serve as a washing line. She, too, suffers from skin problems. Rita's husband, meanwhile, pushes two pieces of corrugated iron to one side to reveal the well. It neither looks nor smells remotely clean.

If the experience of their neighbours is any guide, the outlook is chilling. Half a dozen studies have demonstrated that they are exposed to an unusual degree of toxicity, bringing with it an elevated risk of cancer - of the stomach, rectum, kidney or skin in men, of the uterus and the lymph nodes in women.

If they do fall seriously ill, they will somehow have to find the money for a proper biopsy and course of treatment in Quito, the Ecuadorian capital, which is an 11 or 12-hour bus ride away. There is no nearer hospital. Most likely, they will go to Quito infrequently or not at all, relying instead on a thinly spread team of local team nurses with only antibiotics and painkillers. Rita Maldonado's grim demeanour is partly, no doubt, prompted by awareness of what might await her. Yet her options are slim-to-non-existent. "We can't go anywhere else," she says plaintively, "because it is contaminated everywhere." Everyone in this part of Ecuador knows people who have died - often in horrible pain - and everyone blames it squarely on the shocking legacy of 20 years of oil exploration by a subsidiary of Texaco, in a joint venture with the Ecuadorian state oil company.

The oilmen dumped their heavy sludge in more than 600 unlined open pits and flushed as much as 20 billion gallons of waste water directly into the area's once pristine rivers and wetlands. Environmentalists estimate that some 2.5 million acres of rainforest - half of the original oil concession, covering an area from just below the Colombian border down to the Napo river, a tributary of the Amazon, and beyond - were either compromised or effectively destroyed in the search for the jungle's very own black gold.

The oil executives didn't bother with the now-standard industry practice of re-injecting the waste products into the earth. Even after they pulled out, they bequeathed to the area an infrastructure of outmoded machinery and creaky, rusting pipes prone to further leaks.

Texaco left Ecuador in 1992, which might seem a long time ago. But the devastating impact on the area becomes more apparent with every passing year. "This is as bad as Chernobyl because over time people are getting sicker and sicker," said Nathalie Weemaels, a Belgian agricultural engineer based in Quito who has been very active in resisting oil exploration in the Amazon. "The impact is cumulative - the cancer comes out with time."

This is an overwhelmingly agricultural area, where small farmers keep pigs and chickens around their houses and coconuts and starfruit grow in abundance in their gardens. Now the fruit, and the livestock, are as poisoned as the humans. Animals and, occasionally, children, stumble into the waste pits. The produce is as suspect as the water supply. Sometimes, when locals cut open slaughtered animals in preparation for cooking, they say they can smell the hydrocarbon fumes on the raw flesh.

Texaco's experience in Ecuador has become notorious in the oil industry for a couple of reasons. First, because it has become a textbook case of how not to go about extracting energy resources from an area of Third World wilderness. And second, because it has become the subject of an extraordinary lawsuit that started in US courts more than a decade ago and has now moved to Ecuador, where the authorities are slowly gathering evidence of contamination at more than 120 wells and sludge pits and listening to arguments from the two sides on the validity and competence of their respective scientific studies.

To environmentalists and other activists working to defend the Amazon against incursions by multinational energy companies, what has been perpetrated in the Ecuadorian jungle is a form of slow-motion genocide. Indigenous tribes have seen their numbers shrivel to almost nothing, either because their people have fled the area or because they have succumbed to disease and death. They say the spillages amount to the equivalent of two Exxon Valdez disasters - a reference to the oil tanker that ran aground off Alaska in 1988 - and will take at least $6bn (£3.1bn) to clean up. That is the figure they are seeking to retrieve by way of compensation in the courts.

"The first time I got off the bus in Lago Agrio [the area's main town], I stepped right into oil that was running through the streets. I knew then that I had to fight against this outrage," said Luis Yanza, now a leading voice in the locally-based Amazon Defence Coalition. "It may take us many more years to achieve justice, but we're not going to back down until we have it."

Texaco, now part of ChevronTexaco, does not deny that contamination may have occurred. But it argues it has more than met its obligations, particularly in the wake of a $40m payment it made to the Ecuadorian government in 1995 to cover remediation costs. Any further problems, it says, are the responsibility of PetroEcuador, the state oil company which has managed all assets in the protected area since their joint agreement was dissolved.

The two sides will confront each other today in what has become an annual ritual at the ChevronTexaco shareholders' meeting in San Ramon, California. Community leaders from the Amazon, along with Bianca Jagger and a clutch of other activist celebrities, will be in the forefront of protests to denounce the company they refer to as "Toxico" and to demand meaningful reparations as quickly as possible so that people don't keep dying. Until now, all they have received are aggressive denials of responsibility.

When the prospectors first came to the region in the early 1960s, they told the local populations that oil would bring them unimaginable wealth, but it didn't work out that way. Locals were certainly employed, and earned modestly above the average subsistence wage, but they were restricted almost entirely to unskilled jobs, and then predominantly in the early seismic testing phases of exploration. The technicians and engineers were brought in from Ecuador's cities on the other side of the Andes, or from overseas.

Texaco oversaw a road-building programme, but it was designed exclusively to meet oil extraction needs. The asphalt abruptly stops where the oil trucks and tankers do not need to travel. Of all the billions of dollars pumped into the region, not a cent was spent on improving communications with the rest of the country. Much of the revenue Ecuador generated from the oil went towards paying off its foreign debt, leaving little or nothing for education, health or other essential local services, much less environmental protection.

Oil quite literally took over the jungle. The roads are lined with anything from a single pipe to a cluster of more than 20. Most people have had to build gravel ramps to get over the pipes into their property. In the early days, the company not only showed no signs of caring about leakages and contamination. It even sprayed the streets and roads with oil to keep the dust down.

Humberto Piaguaje, a leader of the tiny Secoya tribe, remembers running barefoot on oil-slicked streets as a child, a radical change from the old life of the rainforest in which no hint of modern life penetrated. "The rainforest had it all," he recounted. "It was our market, our pharmacy, our home. The souls of the great spirits of the rainforest protected us. When I was four years old I saw trucks and helicopters for the first time. We didn't know what was happening or what this portended for the future - they told us oil was a form of wealth. But we thought, how is it possible they are taking the blood from our ancestors living underground in the forests?"

Despite the contentions of Texaco's lawyers, there is nothing subtle about the way the contamination occurred. Above the small town of San Carlos, a rudimentary barbed-wire fence rings an unlined pit set among the trees. From there, it is a clear downhill run to the Huamagacu river, where the women of the town do their washing. Children often come here to swim, too.

"Seventy-five per cent of the children here have skin problems - abscesses and pus spots and raw, itchy skin," said Rosa Moreno, one of four field nurses in the town. "Plenty of others have skin or respiratory problems. Some of them lose their hair. We've had 12 people here die of cancer." San Carlos, not far from a well and pumping station centre called Sacha, has been the community most intently studied by medical professionals, thanks to a European couple, Miguel San Sebastian and Anna-Karin Hurtig, who have meticulously gathered data on the town.

It is almost impossible to make a definitive link between environmental blight and a cancer cluster - a point Texaco has rammed home in court at every opportunity - but the two doctors have demonstrated over and over that San Carlos's cancer rates are dramatically higher than in similar communities untouched by oil pollution. Conditions such as childhood leukaemia were all but unknown in the area until the oilmen arrived. Now the leukaemia has taken on the proportions of a small epidemic, with 91 confirmed cases and counting.

"We have many very sick people," Ms Moreno said. "We don't even know what is wrong with them because in many cases they are not able to see a doctor. For the most part, there are no confirmed diagnoses." She explained how she routinely warns new mothers not to bathe their babies. If they do, their skin becomes angry and red and breaks out in spots. The babies develop hacking coughs, as well as diarrhoea and fever.

Because of the publicity generated by the medical studies, San Carlos now receives piped water for about one-eighth of its 3,000 people - an improvement, for sure, if not a totally satisfactory one because the piped water is contaminated by raw sewage. The water situation remains dire almost everywhere else, Ms Moreno said, and the remediation effort undertaken in the mid-1990s is laughable because the pits were not cleaned at all, merely concealed. "If you dig just a little you find oil again," she said.

The Texaco oil fields are not the only places in the Ecuadorian Amazon which face ecological and humanitarian disaster. Already, a clutch of foreign companies is pushing to open up areas deeper in the jungle - including areas theoretically protected by the state because they are inside the Yasuni National Park which stretches over hundreds of thousands of acres in south-eastern Ecuador. Already, members of the Huaorani tribe, living under the shadow of a project overseen by a large European company, are complaining of gastro-intestinal disorders, breathing difficulties and dermatitis - because of what they and environmental activists have reported as leaks into the groundwater.

A multi-nation inspection team which went into the Yasuni National Park last summer, with full permission from park authorities, to look at fields operated by the Spanish company Repsol, was intercepted by private security guards and thrown out. Repsol, like almost every other oil company in Ecuador, has a policy of keeping all outsiders away from its operations. "Indigenous life is being snuffed out," said Mr Piaguaje, the Secoya leader. "We are tired, but we have to keep fighting. We have to fight for the lives of our generation."