For Sultana Javed, one of dozens of residents living without proper sanitation on her street in the Orangi Town slum, the final straw came when her toddler daughter fell into the soak pit where the family disposed of their waste.
Since moving to the Gulshan-e-Zia area of the slum in Karachi nine years earlier, Javed had poured waste into the soak pit, a porous chamber that lets sewage soak into the ground and is often used by communities that lack toilets.
Javed, whose son caught dengue fever from mosquitoes near the pit outside their home, began mobilising others among 22 families on her street to install their own sewerage system.
“We are fed up with stench of wastewater and frequent mosquito-borne diseases like malaria and dengue fever. So, we have decided to lay a sewerage pipeline in our street on a self-help basis,” Javed, 45, told the Thomson Reuters Foundation.
Orangi is widely cited as Asia’s largest slum and sprawls over 8,000 acres — the equivalent of about 4,500 Wembley football pitches — in the port city of Karachi in northwestern Sindh province.
The settlement’s population exploded in the early 1970s, when thousands of people migrated from East Pakistan after the 1971 war of independence, which led to the establishment of the Republic of Bangladesh.
Today, Orangi’s population is believed to have reached around 2.4mn although no one knows the exact figure since Pakistan’s last national census was held in 1998.
Known locally as “katchi abadis”, the first informal settlements emerged in the wake of the Indo-Pakistan war of 1947, which led to a huge influx of refugees.
Unable to cope with the numbers — by 1950, the population had increased to 1mn from 400,000 — the government issued refugees with “slips” giving them permission settle on any vacant land.
By the 1970s, when Orangi’s population exploded, the settlements had won a quasi acceptance from the government, which was unable to provide services or enough housing.
A system of upgrading and land titling was introduced, giving some residents a little more security — and community-driven upgrading projects a greater chance of success.
Activists estimate that about 60% of Karachi’s total population of 15mn now live in shanty towns.
Unlike in many other slums worldwide, however, the lack of services — not housing — is the major problem.
In Orangi Town, communities built two and three-room houses out of concrete blocks manufactured locally, activists say.
Each house is home to between eight and 10 people and an informal economy of micro businesses has emerged as residents have created a livelihood working from their homes.
As the slum population has increased, residents have been cutting into the hills that surround the settlements, destroying natural bushland around it and creating swathes of barren land.
Despite the poverty, bustling markets dot the streets and surrounding industrial areas offer some employment for unskilled workers.
In 1980, the development expert and entrepreneur, Akhtar Hameed Khan, observed how many communities were self-organising to fill the gap in services — from building homes and schools to water delivery — and launched the Orangi Pilot Project (OPP).
Now globally renowned, the project has not only led the DIY sewerage projects which continue to expand to this day, but has built a network to manage a plethora of programmes that range from micro credit to water supply, to women’s savings schemes.
OPP’s director Saleem Aleemuddin told the Thomson Reuters Foundation that when activists began working in the area in 1980, the lack of sanitation was the most “obvious” and “problematic” area for residents.
While it took the OPP around six months to convince local residents to invest and pay for the installation of the first sewerage line on their street, it was not long before people were taking their lead and organising themselves.
“Since the government gets almost nothing in revenue from the slum, it therefore pays the least interest to its developments too,” Aleemuddin said.
“In fact, people in the town now consider the streets as part of their homes because they have invested in them and that’s why they maintain and clean the sewers too.”
Nearly three decades on, the OPP has not only managed to ensure that more than 90 % of Orangi Town’s nearly 8,000 streets and lanes have sewer pipes — all installed by residents — but has developed a network of collaborators drawing in skills from a wide variety of other non-government organisations.
Training to map and document drainage channels is provided to young people as are programmes that equip community architects, technicians and surveyors to work in the area.
So far, say OPP activists, around 553 of the more than 2,700 Orangi Town settlements are documented.
To date, according to OPP statistics, 96% of the settlement’s 112,562 households have latrines, with residents footing the total bill for the sewage system of Rs132,026,807. 
In Gulshan-el-Zia, Javed and her neighbours decided that to kick-start their works, they needed to choose one person to lead the project and nominated 28-year-old Saleem Khan.
He will not only take charge of planning but will collect residents’ money and contributions for their new sewer and pipeline.
Khan will then work closely with OPP specialists who provide local communities with expert design advice, as well as the technical and engineering support to install the new system.
“I am sacrificing my time and energy to clean my street of the wastewater and protect people from diseases,” Khan said.
“It isn’t an easy job but I hope to get it done in the next couple of weeks with the co-operation and trust of the neighbours.”
Each household plans to share the total cost of Rs65,679 for materials to build the pipeline, which will service the entire street.
Everyone in the family chips in to do the digging and laying work, including women and children.
With just a handful of local schools, most families cannot afford transport costs out of the slum and many young people work with their parents earning meagre incomes from small businesses like weaving and embroidery.
Residents don’t just pay for the installation of the pipes, however, they also take responsibility for their maintenance.
Khan told the Thomson Reuters Foundation that manholes are to be installed at 30 foot intervals along the street to ensure residents have easy access to connections and can also monitor and maintain their pipes themselves.