Red mud shows how far water levels have fallen in Jaguari Reservoir, part of the Cantareira System that supplies half of São Paulo, Brazil. (Dom Phillips/The Washington Post)

Seen from a micro-light aircraft, flying low near this small town in Brazil’s interior, the scale of the water crisis blighting São Paulo, a megalopolis 40 miles away, was frighteningly clear. Four of the five reservoirs in an interlinked system that supplies 6.5 million people, more than a third of its metropolitan population, were vividly depleted. Caked red banks of exposed earth showed just how low the water levels had fallen.

Parts of the Jaguari Reservoir, the highest in what is called the Cantareira System, were so dried out that plants had begun growing on the rocks around a blue pleasure boat, marooned near a wooden landing dock hundreds of yards from any water. A stagnant brown puddle did not trouble the sluice gates of a dam.

[Related: How a bird’s-eye view drives home the extent of Sao Paulo’s drought]

Boat jetties stretched forlornly across banks of red mud from the luxury houses that used to sit by the water’s edge in the adjoining Jacareí Reservoir. Although there was more water in two other lower-level reservoirs, there were also dried-up inlets and red, exposed banks, and the Atibaia River was in places just a muddy eddy.

The biggest city in South America has been stuck in a spiraling water crisis since the summer rains failed to fall last December and January — the driest summer in 84 years. An exceptionally dry winter since then has compounded the problem.

Now, as scientists debate whether Amazon deforestation is to blame, residents across São Paulo complain of regular shutoffs to their water supply while the state government and the water company deny that rationing is going on.

And despite rain in recent days, the water level keeps falling. Cantareira System reservoirs are at a tenth of their normal level. And a full summer’s rainfall — if it should occur in the season beginning next month — will not be enough to refill them.

“The situation is serious and demands the collaboration of all,” São Paulo water company ­SABESP said in an e-mail. “Recuperation of the level of the reservoirs depends on the intensity of the rains.”

But critics say the state government, which controls the water company, played down the crisis because of October’s elections, in which the state’s governor, Geraldo Alckmin, was reelected. Critics say SABESP has failed to keep the population properly informed and to introduce enough effective measures to reduce consumption.

“It is not just the lack of water, which is critical, it is also not knowing how to manage the crisis,” said Carlos de Oliveira of the Brazilian Consumer Defense Institute in São Paulo. The institute only recently received key maps outlining the worst-hit areas — but they did not feature streets, just gradients. “Instead of supplying information, SABESP blames the consumer,” he said.

The water company said there is no rationing or rotating of the water supply — just nightly reductions in pressure to cut losses. Nobody believes it.

“There is rationing,” said Paulo Santos, manager of the elegant Condomínio Louvre building in São Paulo’s center, which has 320 apartments and 45 shops. Water is cut off most nights, starting about 10 p.m., Santos said. He maintains supply by keeping a 12,000-gallon tank full and is installing tanks to capture rainfall on a roof. “The residents are worried. They keep asking about the water,” he said.

Atibainha River, which supplies the city of Campinas with some of its water supply. (Dom Phillips/The Washington Post)

SABESP introduced a discount in February for customers who reduced consumption, and 76 percent are taking advantage. The company’s representatives have visited 30,000 apartment buildings, and eight advertising campaigns have been launched to encourage customers to reduce consumption.

Nine months after the crisis began, the company presented a $1.3 billion infrastructure proposal to the federal government “to guarantee supply security.” In the next few days, it will begin pumping the second quota of “dead water” — billions of gallons that lie beneath the usual capture pumps in the Cantareira System. Two water-recycling facilities and 29 new reserves have just been announced.

“These works that are being done now should already be ready,” said Benedito Braga, president of the World Water Council in São Paulo. “The problem is cultural. Brazilians leave everything to the last minute. Only when the situation is absolutely critical do they start to make arrangements, economize water.”

The worst drought in a century is principally to blame, Braga said. But measures such as these, taken in time, could have alleviated it, he said.

São Paulo is an endless, chaotic sprawl that has grown, unchecked, for decades. With a population of 19 million in its metropolitan area, it is now facing water-supply problems that U.S. cities dealt with decades ago, said Richard Palmer, head of the Department of Civil and Environmental Engineering at the University of Massachusetts.

Palmer visited Brazil in May. “I was very surprised at the confidence that SABESP showed in being able to manage this crisis without involving more people,” he said. “I couldn’t imagine another international major city allowing itself to get to such a precarious point without having introduced water use restrictions.”

Antonio Nobre, a researcher at Brazil’s National Institute for Space Research and its National Institute for Amazonian Research, wrote in an e-mail that deforestation might be connected to the drought.

In October, Nobre published a scientific assessment report, which argued that clear-cutting has altered the Amazon forest’s climate — as evidenced by droughts in 2005 and 2010. The forest functions as a “biotic pump,” it said, channeling moisture down to São Paulo via “aerial rivers” that bounce off the Andes wall.

But Augusto Pereira, a professor at the Department of Atmospheric Sciences at the University of São Paulo, blamed an area of high pressure that formed over the South Atlantic for this and earlier droughts. “This is recurring,” he said.

In the bare, concrete São José Operário church hall in Jardim Damasceno, on the northern edge of São Paulo, residents who gathered after a fitness class on a recent day said their water supply failed regularly — for some at night, for others in the day. Outlying, lower-income areas like this have been hardest hit by dry taps. And Jardim Damasceno is a chaotic jumble of poverty — the breeze-block shacks of Brazilian slums teetering over concrete housing blocks, near a small square dominated by the drug trade.

Those living higher up in the favela fared worst.

“It is too much,” said Euriba Alves, 71. “Water is life.” Her neighbor Josefa Olegario, 70, who runs a small bar, said her tap water often flowed out white and milky. “I let it settle a bit,” she said. Roberta da Silva, 39, a health visitor, cut her water bills by reducing consumption, but she scoffed at SABESP’s insistence that there is no rationing. “It is a reality,” she said. “They know.”

In her neat, one-floor house beside the church, Eliete Silva, 64, remembered the torrential floods that swept away her house eight years ago, for the second time. “The water came in the window,” she said. “It used to rain much more.” Now the water does not flow, even through the pipes, at night, said her daughter Edna, 32. She was receptive to the idea that Amazon deforestation could be a factor. But she blamed the government. “They did not take measures, it got to the point it did, and the people suffer,” she said.