NAIROBI, Kenya -- The stench rising from a fly infested sewage ditch is worsened by the scorching sun. But for some enterprising residents, it's the smell of progress.

Some have helped construct a network of public latrines that recycle human waste into gas for cooking and light. Others, assisted by a Swiss aid organization, use sunlight to purify drinking water, dramatically slashing cases of waterborne disease. There's an urgent need for projects like these.

For up to a million residents in Kibera, it's harder than ever to scrape together a dollar for cornflour and wilted cabbage for one meal a day. Staple food prices in the capital have doubled in six months. And the price of coal for cooking has increased by a quarter.

The "bio-latrines" are built next to a school for orphans. Around 600 people use them, generating enough gas to cook for 68 orphans next door and provide hot water for a shower block serving hundreds of people.

"Before the biogas came, the kids were just having cold washes in the winter and now they have hot water at school they don't have so many colds," said Bernard Asanya, the school director.

The money the school saved on cooking charcoal has paid for the salaries of two extra teachers, Asanya said, watching dozens of grubby, bright eyed toddlers chase each other around the bare dirt yard.

The project, adapted from a design produced in Tanzania, is funded by an alliance of international donors and run by the communities themselves.

Residents pay three cents to use one of eight drop toilets installed around a buried tank. The waste goes into an airtight "biodigester," where methane gas filters into an upper tank. The gas can be used to light stoves, turn on lamps or heat water, although it is not yet pumped to individual homes.

Solid waste is treated and filtered through reed beds before being collected to be sold as fertilizer.

The trickle of coins pays cleaners and a caretaker and funds other bio-gas projects. The first center built four years ago in Kibera proved so successful that there are now 34 other bio-gas projects in various stages of completion around Kenya.

"You know fuel is expensive, that's why we came up with the idea of generating energy from human waste," said community outreach worker Stephen Otondo.

If another 200 people a day came to spend a few pennies, there would be enough gas to light a street lamp in this slum where there has never been electricity. That would mean safer streets in a part of town where glue-sniffing gangsters lurk in the alleys after dark.

One big benefit of the bio-latrines is the fall in what residents call "flying toilets" -- plastic bags that slum residents sometimes use to relieve themselves and then fling out of shack doors into alleys, occasionally catching unwary passers-by.

But not everyone in the slums has a bio-latrine nearby. Often, trickles of sewage in the streets become streams choked with garbage, used condoms and rotting food. Bedraggled puppies splash in the waste.

These rivers of disease often run parallel with cracked, corroded pipes bringing water to communal taps. Germs enter the water supply through the leaks, sickening children whose parents cannot afford doctor fees.

That's where Kaltouma Tahir and her water purification project come in.

The 52-year-old mother of six still remembers watching her neighbor's 3-year-old son Gilbert get sick and die after contracting diarrhea from drinking dirty water seven years ago.

Shortly afterward, she helped start a pilot project run by the Swiss aid organization that purifies water using the sun's ultraviolet rays. Now she shows each neighbor how to place clear plastic bottles with the contaminated piped water onto corrugated metal roofs.

They call her Mama Sodis, after the organization's name -- shortened from Solar Water Disinfection. The one liter bottles only cost a few cents each and are reusable.

Tests conducted in Swiss labs showed six hours in the sunshine or two days if it's overcast is enough light to kill off almost all germs that cause diseases, including cholera, typhoid, dysentery, polio and hepatitis.

Kenyan chemist David Kariuki says that in areas where the project has taken off, local clinics have seen a 90 percent reduction in the number of patients with waterborne diseases. Children don't miss school and parents don't miss work. Savings that would have gone to medicine are spent on school books or extra food instead.

The Kenya water project has grown from three staff members to 24, reaching 65,000 households and 15 schools in Kibera.

Worldwide, the technique is used by about 2 million people in around 30 countries, but it's still a small fraction of the 1.1 billion people who need safe water.

Now Mama Sodis and her colleagues hope to set up a regional center in Kibera where other Africans can come and learn about their success. She says in the seven years since the program was launched, deaths of neighborhood children from waterborne diseases have fallen from about 20 per year to two or three.

For her, progress isn't only about numbers but about convincing people they can change their lives.

Gilbert's mother, a tomato seller, left the slums brokenhearted after her son died. But along with the memories of her dimpled 3-year-old, she also took two living children -- and a supply of clean plastic bottles.

On the Net: www.sodis.ch