Pakistan’s government has no interest in providing clean water to the 700,000 residents of Karachi’s biggest slum. Step forward a 26-year-old British woman with a tablet she says could purify water that kills 20,000 children a year. In the third part of her series on water, Annabel Symington reports

Read the first part of The Samosa's water series here

Read part two here

Machar Colony lies beyond the railway tracks in Karachi, Pakistan. As you delve into the slum, Karachi’s cosmopolitan business centre, luxurious shopping malls and modern housing all fade from memory. They are not part of life here.

Machar Colony is Karachi’s biggest slum, where hundreds of thousands of small cement houses cling to the sandy coastal ground. The slum covers an area of approximately four kilometres square, about twice the size of the City of London. Like most slums around the world, Machar Colony is illegal, and is consistently ignored by government plans to improve the city.

Machar Colony’s 700,000 residents, most of them children aged between 5 and 15 years old, have little access to water, electricity or basic sanitation. The ageing water and sewage pipes in Karachi run close together, one often mixing with the other. Dirty water kills an estimated 20,000 children in Machar Colony each year.

Hema Mukresh, a public relations consultant for the Concern for Children Trust, a charity that works extensively in Machar Colony, explains: “As far as sanitation and clean drinking water is concerned, the situation in Machar Colony is not good, as they don’t have access to both. The water they drink has the main pipeline under a drainage system for the West Wharf and all areas around it, so you can imagine what will be the state of the water they drink.”

But there is a new initiative seeking to remedy Karachi’s slums’ water problem – a for-profit business initiative called Saafwater. Named after the Urdu and Hindu word ‘saaf’, meaning ‘clean’, Saafwater was set up by British engineer Sarah Bird, 26, and sells water-purifying tablets to Karachi’s slum dwellers.

Saafwater has been working in Machar Colony since the summer of 2008, but came up against some unexpected obstacles when it first started selling its water-purifying tablets in the slum.

"I cannot take these tablets as my husband has said no," Shahida, a young housewife in Machar Colony, told Saafwater ‘sales lady’ Farooq Sultana. Shahida's husband believed the water-purifying tablets were birth control pills.

"People here have this misconception that we are selling them contraceptive pills and men think that somehow these tablets will interfere with their reproductive systems," says Sultana.

Despite the initial scepticism towards Saafwater’s water-purifying tablets, they are developing a dedicated customer base. Saafwater currently sells its tablets to 100 families on a regular basis, but by the end of 2009 Sarah Bird hopes to have expanded its customer base to 20,000 with more than 150 sales ladies.

Saafwater employs local women to sell the tablets. The sales ladies receive a performance-based salary according to the number of customers they have. The target earning for Saafwater’s saleswomen is 9,000 rupees (£65) a month, nearly four times the average monthly income in the slum. The top sales representative in each area also receives an annual bonus of 100,000 rupees (£730).

The beginnings of Saafwater lie at the Massachusetts Institute of Technology, where Sarah studied and worked as a research assistant. In 2007, Sarah and her team won $10,000 in MIT’s $100k Entrepreneurship Competition for their work with Saafwater. This money allowed the company to get off the ground and begin its pilot project in Karachi’s slums. The idea behind Saafwater is to develop a profitable distribution network that will eventually expand to other low-income urban communities across Asia.

Saafwater has been set up as a business rather than as a non-profit charity. Bird says the business structure creates a “profit motive” within Saafwater, which is lacking in non-profit organisations, and this promotes sustainability and growth. “We are reliant on our customers,” she explains. “And as long as we are providing a valuable service to them we are going to be able to not only sustain ourselves but also grow. That’s a very powerful thing when you think about the size of the problem we are trying to address.” Currently, one in six people around the world lack access to clean drinking water.

The Saafwater tablets use chlorine, an established water purification method used in sanitation systems across the developed and developing world. Chlorine is a cheap way to clean water - a week's supply of Saafwater's chlorine tablets for a family of five costs Rs30 (less than 25p), and each tablet purifies up to 25 litres of water.

Despite Sarah’s engineering background and interest in new technologies, she says that sustainability is in many ways more important than innovation when it comes to meeting the basic needs of people around the world: “I was always very excited about technology. But then at some point I realised that it’s all well and good to create new technologies but those new technologies aren’t getting out there. So, what really caught my attention was not how can we make a better gadget to clean water, but how can we get existing technologies, that work, to the billions of people who need it.”