Parapa, a semi-skilled electrician, lived with his parents, two brothers, their wives and two children in a room of 48 square feet. If half the family members slept on their sides, they could just about fit. But as the only single male, Parapa felt a dreadful gooseberry. Like Shashi, he is a member of the local branch of the Communist Party of India (Marxist), which tells Dharavi’s youths not to marry unless they can support a family. Wretched nonetheless at the nightly coupling around him, Parapa began sleeping in the alley outside—and drinking heavily.

As Bombay boomed, on the back of its port and textile mills, poor peasants flowed in from the land. During periodic famines—including one in Bengal in 1943 that killed 3m people—they came in spate. Dharavi is where these migrants claimed—or reclaimed—a plot. Shashi’s parents were propelled from Karnataka by a drought, arriving in the city with five small children in 1976. “In the village we were starving,” says his mother, Shantabai, creator of the tasty bean curry. “Here, we were poor, but we could eat.”

During a four-day stay in Dharavi, as the guest of Shashi and his friends, your correspondent heard many such tales: of hard times, facing up and getting by. The narrators were sometimes bitter or suspicious, but mostly friendly, almost invariably courteous, and occasionally, like Parapa, very funny. If poverty can seem dehumanising from afar—especially in much reporting on it—up close Dharavi, which is allegedly Asia’s biggest slum, is vibrantly and triumphantly alive.

With this history, Dharavi’s population is diverse. Tamils, Andhras, Assamese, Biharis, Bengalis and local Maharatis; all India’s peoples are here. Perhaps a little over half belong to India’s poorest groups: dalits and Muslims. They tend to live semi-ghettoised, as in Shiva Shakti Nagar, within the same language group. Indeed, the poorer Dharavi’s residents are, the more caste-sensitive they are likely to be. Mr Kadam is a dhor, of the dalit tanning caste. Yet as his business thrived, his family became middle class, a powerful identity. Last year Mr Kadam exported 25,000 leather belts to Wal-Mart in America. He has moved his family from Dharavi to a smart suburb of Mumbai. Laughing proudly, he says his teenage son refuses to visit the ancestral factory, which he considers dirty.

The four children of Venkatesh Dhobi, all aged ten years and under, cannot shun their ancestral pool of filth. They work every day in this well of brown water, beside a litter-strewn railway line. They pass unwashed clothes into the pool, where 20 adult dhobis—of the dalit washer caste—soak and scrub them. With an explosive grunt to keep rhythmic time—a sound not unlike that emitted by Japanese Noh theatre actors—together they thwack the heavy sopping clothes onto smooth stones. The children then strew them between the railway tracks to dry. They are the fifth generation of Dhobis to work at this pool. The first, says Mr Dhobi, was his great-grandmother, who arrived from Mehaboob Nagar, in Andhra Pradesh, a century ago. “For 100 years, we have served this city,” says Mr Dhobi, a short 35-year-old with the torso of an underpants model. And yet their rural roots have survived. All the dhobis in the pool—which is called Dhobi Ghat—are from Mehaboob Nagar. Aged 14, Mr Dhobi was married there to a local girl. The big changes of the past century, in his view, seem to be that Dhobi Ghat has got much dirtier and people send fewer clothes to be washed in it. India’s swelling middle class—people like Mr Kadam—prefer washing-machines. Together, Mr Dhobi, his wife and four children earn less than 200 rupees a day.

With reliable power and water, many of Dharavi’s residents have been able to start businesses inside the slum. In this they had a great advantage—the other main reason for the slum’s rise. As Bombay expanded, so Dharavi became the heart of India’s commercial capital. Indeed, in a city of notoriously rotten infrastructure, the slum is a transport hub. It is sandwiched between Mumbai’s two main railway lines and ringed by six stations. In addition, Dharavi’s hutment industrialists enjoy the competitive advantages of slum-life: cheap labour and an environment where government inspectors fear to tread.

For thousands of men like these, Dharavi is a wonderful opportunity. But for millions of Mumbaikers, it represents a cost. Their city, South Asia’s biggest, is choking. Its infrastructure is a crumbling disaster. And yet over the next decade, the UN says the population of Mumbai will almost double, making it the world’s second-biggest city after Tokyo. Massive urban redevelopment is required—starting with Dharavi, at the city’s heart. By one estimate, the slum’s land alone represents $10 billion in dead capital.

So, these may be the last days for Dharavi. If so, much that is wretched will be lost. And, who knows, maybe something better will arise. Most of the slum-dwellers doubt this. And a few high-rise blocks, scattered across the slum, do not inspire great hope. Many are half-built and slowly mildewing. Lots of their residents, it is said, have already sold up illegally, and moved back to the slums, seeking things that town-planners cannot provide: a sense of history, community and freedom. Dharavi has these, as well as many horrible problems. It is organic and miraculously harmonious. It is intensely human. Unlike the random tower-blocks, Dharavi makes sense.