NEW DELHI -- The United Nations is celebrating an Indian government program officials say can be a model for other low-income and developing countries at a summit this week in New Delhi. But in Taimoor Nagar, a slum just outside one of the city's poshest neighbourhoods, hundreds of people rely on a single public toilet, underscoring the challenges that remain for India's urban poor.

The numbers in the government's ambitious Swachh Bharat, or Clean India, program are staggering. India's population of 1.3 billion accounted for 60 per cent of the world's open defecation in 2014, when Prime Minister Narendra Modi came to power, but that dropped to 20 per cent by 2018.

The summit -- with a keynote address by UN Secretary-General Antonio Guterres on Tuesday -- overshadows the struggles with open defecation that remain in the heart of India's capital.

The US$20 billion program concludes in 2019, timed to coincide with the 150th anniversary of Mahatma Gandhi's birth. The freedom fighter wrote in 1925 that many diseases in India were caused by a "bad habit of disposing of excreta anywhere and everywhere."

In many parts of Delhi, Gandhi could have been writing about 2018.

Huge sums have been spent on a marketing blitz featuring videos of Bollywood stars sweeping the streets. Modi launched the program in 2014, appearing before a battery of journalists to sweep the courtyard of a police station in a low-caste Dalit residential colony in central Delhi.

Gandhi's signature wireframe glasses, the Swachh Bharat symbol, have been stamped into Delhi's cityscape, appearing on the sides of bus stations, on newly built public bathrooms and on huge billboards.

But aside from a Swachh Bharat banner residents say was hung recently at the entrance to the portable toilet and wash basins in Taimoor Nagar, residents have seen little evidence of the program's gains.

Sometimes the toilet is too dark, too dirty or too expensive -- it costs 5 rupees or 7 cents per person -- for Sapna, a maid who goes by one name, and her husband and four children to use.

"Because so many people use one bathroom, disease spreads fast," Sapna said as flies and mosquitoes flew in and out of her family's one-room hut. Toilet fees and the cost of medicine eat into her family's 13,000-rupee ($179) monthly budget.

The children and women of Taimoor Nagar still use the site of a former bathroom complex torn down years ago where people store and sort recyclable material fished out of a trash-clogged nearby canal.

Rajaram Kamat, a samosa vendor who has lived in the community for more than 30 years, estimates that his household is among just one in four to have a toilet.

Kamat says a government-built sewer line carries waste to the canal, but that no one cleans the putrid waterway.

It is impossible to say how many people live in Taimoor Nagar or other communities the South Delhi Municipal Corporation has deemed "unauthorized."

Shri Vinod Kumar Jindal, director of the Swachh Bharat Mission in India's urban areas, said the central government has built 450,000 community toilets in such places and has uploaded their locations onto Google Maps so that women especially can easily find them.

The government's cleanliness campaign has made clearer progress in rural areas, largely due to an inexpensive toilet design invented in India four decades ago -- a twin-pit latrine system built from brick where waste shifts from one pit to another and becomes compost over time.

In four years, half a billion people have stopped openly defecating in India, in part due to the 490,000 community "motivators" who have encouraged people to use the nearly 86 million toilets that have been built in rural areas. UNICEF has assisted in teaching the design and building of these systems to thousands of women villagers, some of whom have turned the work into a full-time job.

In Jharkhand, a state in eastern India, Sima Kujoor and other women in her village formed a committee to request government funds and receive training to build twin-pit toilets.

"The village earlier was a little bit in bad shape, filthy. Now there's a lot of cleanliness and hygiene," Kujoor said, adding that they recruited women from each household to demonstrate how to use and clean a toilet. The committee has also created an incentive system, paying people to report when they see others openly defecate with fines assessed against the perpetrators.

But in Delhi and other urban areas, fecal sludge goes into sewers and septic tanks, most of which are cleaned by hand.

And a stigma over cleaning sludge -- historically a low-caste occupation -- persists in India.

UNICEF's executive director, Henrietta Fore, told The Associated Press on Monday that the water and sanitation industry could potentially employ huge numbers of India's urban poor, destigmatizing the work.

"If you can give it a status, a prestige, professionalism, people will be drawn to it," she said.

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AP editorial assistant Chonchui Ngashangva contributed to this report