Jockin Arputham with two of the women he has mobilised to help build toilets in the slum. Credit:Amrit Dhillon Avekar must share a communal lavatory with 50 other families. ''I have to get up at 4am to go to the toilet,'' she says. ''If I leave it till six or seven, I'll have to wait in the queue for two hours.'' Queue for the toilet, wait in line for a bucket of water, hear the sniffles, belches, sighs and grunts of your neighbour, sleep on top of one another, feel the breath of other people on your skin and their odour in your nostrils, constrain your body movements because spreading out an arm will knock someone, travel in insanely crowded trains, and in the summers, roast in unventilated rooms. That is the lot of Avekar and the lot of the 60 per cent of the city's 13 million who live in the slums of one of the world's most densely populated places. These places have inadequate sanitation, light, electricity and water. The communal toilets are clogged. Pigs and street dogs share the same open spaces as children. Typhoid, tuberculosis, dengue fever, malaria and dysentery are rampant. The city's most famous slum, Dharavi, near the airport, contains more than half a million people sprawled across 210 hectares.

Jeeta Avekar in her flat with her husband and daughter. Credit:Amrit Dhillon Housing is the single biggest concern for people - poor, middle class, even the rich. Not that this deters the thousands disgorged from the trains that roll in from other regions of India to seek a better life, lured by the city's fabled riches (it is the richest city in India) and the fact that it is home to Bollywood. Arif Sahani, 26, who sells ''bhel-puri'', a local snack, on the street near the iconic Taj hotel, arrived six years ago from his village in the state of Bihar. He makes enough to get by and to send some back to support his wife, children and parents. Inside Victoria Terminus. Credit:Amrit Dhillon ''My biggest problem is where to put my stall,'' he says. ''People fight over every inch of space. Other street vendors want this spot. It's a struggle every day to make sure I get this spot where there are plenty of tourists,'' he says.

Sahani, like all the others, ended up in a slum. The struggle for access to toilets is Darwinian. Avekar feels ''lucky'' to share a toilet with 50 families. Some 7 million Mumbai residents do not have access to a toilet at all. Life on the street. Credit:Amrit Dhillon The lack of space in Mumbai assaults all the senses. Clogged roads, crowded markets, few open spaces where children can play or lovers kiss, ugly tenements teeming with people, the constant hum of human activity. Mumbai is tiny. It is a peninsula of some 480 square kilometres. In 1990, it had a population density of 15,000 people per square kilometre. Now it is 20,694 per square kilometre. But because the population is unevenly distributed across the city, some areas have a population density of one million people per square kilometre. The figure for Hong Kong is 6415; for Shanghai 6845, for Berlin 3924 and for Sydney 2186. The infrastructure cannot cope. ''This is the highest number of individuals massed together at any spot in the world … two-thirds of the residents are crowded into just 5 per cent of the total area,'' writes author Suketu Mehta in his book on Mumbai, Maximum City.

Only a glimpse of the Arabian Sea offers relief. Only the very rich in their mansions and luxury penthouses can breathe. Everyone else is suffocated by people, dirty air, and cars. One of those cars, a taxi, is Avekar's. Sixteen years ago when her husband suffered a stroke, brought on by acute hypertension, her world collapsed. A woman who had only ever gone out to buy vegetables or visit relatives was suddenly the breadwinner. At first she bought fish from the fishermen and sold it on the streets. But her income was a pittance. Fortunately, she came to hear of an NGO which trains slum women to become taxi drivers. When Avekar started training, some neighbours jeered. ''I wore jeans when driving but I used to go into a public toilet to change into a sari before reaching home because the men would laugh at me for wearing jeans, accusing me of a being a prostitute,'' she says. The timid housewife transformed herself into a feisty, no-nonsense woman who, she says laughing ''can eat anyone alive'' if they trouble her. The only thing she hates is the traffic jams. She has seen ambulances, sirens blaring, unable to move in the dense jams. To ease the congestion, a stunning eight-lane bridge connecting Worli with the suburb of Bandra was built across the Arabian Sea. The bridge is so impressive it has become a tourist attraction, but the logjam continues.

For years now the city has been inching towards implosion. Much has been written on the city's future, veering from obituaries to passionate assertions of its imminent renewal. Intense debates revolve around whether it can become another Singapore, Shanghai or Dubai. Or will the megacity buckle under the weight of its own sewage and sink into the sea? The multitudes are best seen on the local rail network. Every day, more than 8 million people travel, packed like staples, by train. Because of the overcrowding, about 3600 people die and more than 4000 are injured every year. Trains with a capacity of 1500 passengers regularly carry more than 8000. The spectacular Victorian gothic architecture of Victoria Terminus station in Churchgate is a vestige of a time when railway stations awed like cathedrals. It teems with humanity. Nitish Tuli, a 21-year-old software consultant, is waiting for a train to Thane, a township outside the city, just before the volcanic surge of the rush hour when great columns of commuters march from all over the city towards the station. ''On some days it takes two hours to get home, standing all the way. During the rush hour your feet don't need to touch the ground. The crowd just sweeps you along,'' says Tuli. Mumbai's density leaves little room for the living, let alone the dead. For Christians who want burial, the shortage of space is indeed grave. In the film The Lunchbox, which won critical acclaim at Cannes last year, Indian actor Irrfan Khan is shown travelling in a crowded train and muttering about how, having spent a lifetime commuting vertically in packed trains, he will no doubt end up in a vertical grave.

India's stark inequality is at its starkest in Mumbai. The slums are often next to luxury high rise condominiums. Pockets of prosperity are surrounded by areas of mass deprivation. About 40 per cent of India's 52 billionaires live in Mumbai, according to Forbes magazine. A few years ago, the huge tract of land where the old textile mills had stood derelict and empty for decades (Mumbai was once famous as the ''Manchester of the East'') was freed up for developers. In no time at all, the skyline filled with new skyscrapers. The silhouettes of cranes can be seen all over as construction continues apace. A 60-storey twin-tower, the Imperial, with apartments costing as much as $14 million, offers views of the ocean, the racetrack and the golf course. The 53-floor Lodha Bellisimo offers penthouses with swimming pools and ballrooms. And soaring over Altamount Road is the world's most expensive house, owned by the richest man in India, Mukesh Ambani (estimated net worth $22.3 billion), who lives with his wife and three children in the $1 billion, 27-storey building. Widely criticised for being outrageously ostentatious for a city known as ''Slumbai'', the mansion has become a landmark. People still wonder why Ambani chose to erect a weird-looking vertical building when he could have bought a colonial-style bungalow, but it is a fact that Mumbai can grow only vertically. No more land can be reclaimed from the sea. Slum dwellers must be rehoused in the space available. The Indian government has promised to make its cities ''slum-free'' by 2015 but this deadline is regarded as a joke.

If the government has belatedly started thinking about slums, it's because 250 million people are expected to pour into India's cities in the next 20 years. McKinsey & Company India predicts that by 2030, 590 million people will live in cities, nearly twice the population of the US. For the first time in India's history, some states will have more living in cities than in villages. But from the way Mumbai is struggling, this urbanisation - the McKinsey report of 2010 calls it the ''fastest urbanisation the world has ever seen, after China'' - is something the country is not ready for. The cities will be unable to cope with the demand for homes, electricity, water, buses, roads, schools, trains and sewerage. Mumbai is already swollen, on the verge of bursting. Its services cannot cope. McKinsey says that the city's population could double in the next 15 years. In the district of Colaba, where he runs a travel agency, Khalid Ali, 64, is horrified when he reads these projections. He commutes four hours every day. ''We have already reached saturation point. We've got skin-to-skin contact on the trains. How much closer together can we live without going mad? There is nowhere to walk, nowhere to throw a ball or have a picnic,'' said Ali.

Mumbai developers have been constrained in building high rises in the city's residential areas because of a four-decade-old law limiting the height of buildings. But now, under a new policy, they are constructing luxury towers in shanty towns and rehousing the slum-dwellers in tiny new flats the size of an average garage on the same land. Some improvements are happening, thanks to this policy and the efforts of men like Jockin Arputham, 72, who has lived and worked in Dharavi for more than 40 years and is president of the National Slum Dwellers Federation. One of his achievements is getting slum dwellers not to expect the government to build toilets but to mobilise their own skills - a mason, a bricklayer, a plumber - and their resources to build toilets themselves. He makes sure that the grants he receives from the government go to women in Dharavi and other slums. Two such women, housewives-turned-contractors, sit with him in his small office on the edges of Dharavi. The women, Meena Raman and Guddi Bharati, used to sell garlic on the street. As contractors, they have built 50 toilets so far. Arputham is working with the government to rehouse slum dwellers under the new policy. ''Slums have to be accepted and improved, not removed. These are not just buildings, they are homes. A community has been created here,'' he says.

Arputham's main complaint is that the plan is moving too slowly. Officials, he says, refuse to approve the developers' plans without huge bribes. Figures released last September show that since it was set up in 1996, the Slum Rehabilitation Authority has completed only 197 rehousing projects out of the 1524 on the list. Still, if Avekar's dream of a home with a window ever materialises, it has to be in the slum where she lives, not in some far off place. For outsiders, a slum is an ''excrescence'', writes Mehta. But for those living there, it is home. ''I know the people here. They know me,'' says Avekar. ''We all pitch in and help … Sometimes, when I get home from the noisy congested roads and walk into my noisy crowded home, a bit of quiet would be nice. ''But it's impossible - at least not in this lifetime.''

Amrit Dhillon is a Delhi-based writer.