Separated by a road and a viscous finger of black, garbage-choked water, the stilt-house slum of Muara Baru and the BMW car dealership that faces it appear as if from different worlds.

But on December 6, 2025, these two extremes of the Indonesian capital will have something in common as a World Bank study shows that unless action is taken, they and much of the coastal city of 12 million will be submerged by seawater.

Experts have pinpointed that date as the next peak of an 18.6-year astronomical cycle, when sea levels will rise enough to engulf much of Indonesia's low-lying capital.

Climate change is causing sea levels to rise, but the study's authors say the main problem is that Jakarta is sinking under the weight of out-of-control development.

"The major reason for this is not climate change or whatever, but just the sinking of Jakarta," says JanJaap Brinkman, an engineer with Dutch consultancy Delft Hydraulics who worked with the World Bank on the study.

"We can exactly predict to what extent the sea will come into Jakarta."

By 2025, estimates from the Intergovernmental Panel on Climate Change show, sea levels will have risen by only about five centimetres (two inches).

But Brinkman says Jakarta, which spans a flat plain between mountains and coast, will be between 40 and 60 centimetres lower than it is now.

The study shows that without better defences, in 2025 the sea will reach the presidential palace around five kilometres (three miles) inland as well as completely inundating Jakarta's historic old city to the north.

December 6 will be the highest point of the tidal cycle, but Brinkman warns there are likely to be plenty of floods before then.

Brinkman blames the swelling city's over-development, which is compressing the land it is built on.

The problem has been exacerbated by factories, hotels and wealthy residents drilling deep water bores to bypass the city's shambolic water grid, sucking out the groundwater and causing further subsidence.

The World Bank has called for a halt to deep groundwater extraction, and the city administration has raised the price of groundwater but so far there has been little progress.

"If you do nothing about the groundwater problem, parts of Jakarta will sink five metres (by 2025)," Brinkman says.

A glimpse of the future can be seen in the shacks of Muara Baru, where the city's north meets the sea, and where flood levels late last year reached up to two metres.

The few trees that shaded this fishing slum were underwater for so long they are now dead and bare.

Muara Baru is bordered by just the kind of high-rise towers, luxury homes and mega-malls that are pushing the area into the sea.

There is little water to drink in the slum itself -- around 40 percent of Jakarta's population is not connected to the water grid, said Achmad Lanti, the city's water regulator.

Jakarta's water was privatised in 1997 in the hope of improving services. But Lanti said the two foreign operators brought in to run it had failed to live up to pledges to bring water to 75 percent of the population by 2007.

The shortage leaves many Jakartans with limited options: buy the water at a marked-up price, dig for it, or steal it.

Around half of the water from Jakarta's pipes disappears through a combination of leaks and theft, Lanti said.

"Sometimes (those who steal) are only individuals, sometimes they form a kind of organised crime, what I call a water mafia," he said.

In Muara Baru, Sayong, a 65-year-old grandmother, and Aris, who says he is in his 70s, skid down hill holding a push-cart filled with jugs of fresh water.

Each day Sayong fills three carts full of water from a pump and sells it on to other residents. After using the water she needs and selling the rest, Sayong, who lives with two adult children and two grandchildren, said she earns a maximum of 20,000 rupiah (2.20 dollars) a day.

Her tiny income means she has no option but to stay in Muara Baru, where the floods are a constant threat.

"It's serious, I can't sleep because I'm always afraid that there will be flooding from the sea," she says.

The waste-filled canal that runs up to the slum's edge shows the effect of the city's chaotic development.

Massive buildings have taken over natural drainage sites, while human waste and rubbish clog waterways, causing freshwater floods that surge up from the ground during the rainy season.

The drainage system built by the Dutch who once ruled Jakarta is unable to cope with the city's rapid growth, said Hongjoo Hahm, the top infrastructure specialist at the World Bank in Indonesia.

"Every year we get floods," he says. "The scale of the floods (the Dutch) were talking about every 25 years are happening every year."