As Mumbai booms, the poor of its notorious Dharavi slum find themselves living in some of India's hottest real estate.

All cities in India are loud, but nothing matches the 24/7 decibel level of Mumbai, the former Bombay, where the traffic never stops and the horns always honk. Noise, however, is not a problem in Dharavi, the teeming slum of one million souls, where as many as 18,000 people crowd into a single acre (0.4 hectares). By nightfall, deep inside the maze of lanes too narrow even for the putt-putt of auto rickshaws, the slum is as still as a verdant glade. Once you get accustomed to sharing 300 square feet (28 square meters) of floor with 15 humans and an uncounted number of mice, a strange sense of relaxation sets in—ah, at last a moment to think straight.Dharavi is routinely called "the largest slum in Asia," a dubious attribution sometimes conflated into "the largest slum in the world." This is not true. Mexico City's Neza-Chalco-Itza barrio has four times as many people. In Asia, Karachi's Orangi Township has surpassed Dharavi. Even in Mumbai, where about half of the city's swelling 12 million population lives in what is euphemistically referred to as "informal" housing, other slum pockets rival Dharavi in size and squalor.Yet Dharavi remains unique among slums. A neighborhood smack in the heart of Mumbai, it retains the emotional and historical pull of a subcontinental Harlem—a square-mile (three square kilometers) center of all things, geographically, psychologically, spiritually. Its location has also made it hot real estate in Mumbai, a city that epitomizes India's hopes of becoming an economic rival to China. Indeed, on a planet where half of humanity will soon live in cities, the forces at work in Dharavi serve as a window not only on the future of India's burgeoning cities, but on urban space everywhere.Ask any longtime resident—some families have been here for three or more generations—how Dharavi came to be, and they'll say, "We built it." This is not far off. Until the late 19th century, this area of Mumbai was mangrove swamp inhabited by Koli fishermen. When the swamp filled in (with coconut leaves, rotten fish, and human waste), the Kolis were deprived of their fishing grounds—they would soon shift to bootlegging liquor—but room became available for others. The Kumbhars came from Gujarat to establish a potters' colony. Tamils arrived from the south and opened tanneries. Thousands traveled from Uttar Pradesh to work in the booming textile industry. The result is the most diverse of slums, arguably the most diverse neighborhood in Mumbai, India's most diverse city.Stay for a while on the three-foot-wide (one meter) lane of Rajendra Prasad Chawl, and you become acquainted with the rhythms of the place. The morning sound of devotional singing is followed by the rush of water. Until recently few people in Dharavi had water hookups. Residents such as Meera Singh, a wry woman who has lived on the lane for 35 years, used to walk a mile (two kilometers) to get water for the day's cleaning and cooking. At the distant spigot she would have to pay the local "goons" to fill her buckets. This is how it works in the bureaucratic twilight zone of informal housing. Deprived of public services because of their illegal status, slum dwellers often find themselves at the mercy of the "land mafia." There are water goons, electricity goons. In this regard, the residents of Rajendra Prasad Chawl are fortunate. These days, by DIY hook or crook, nearly every household on the street has its own water tap. And today, like every day, residents open their hoses to wash down the lane as they stand in the doorways of their homes to brush their teeth.This is how Dharavi wakes up. On 90 Feet Road, named for its alleged width (even if 60 Feet Road, the slum's other main drag, is considerably wider), the cab drivers coax their battered Fiats to life. In the potters' neighborhood, black smoke is already pouring from six-foot-square (one square meter) kilns. By the mucky industrial canal, the recyclers are in full swing. In Dharavi nothing is considered garbage. Ruined plastic toys are tossed into massive grinders, chopped into tiny pieces, melted down into multicolored pellets, ready to be refashioned into knockoff Barbie dolls. Here every cardboard box or 55-gallon (208 liters) oil drum has another life, and another one after that.