In the slums of Dhaka, Bangladesh, even the simple act of giving your child a glass of water requires an act of faith.
Parvin, a mother of four, knows this all too well. Five months ago, her 3-year old son Rudoy drank some water. Three days later, he was dead of diarrhea, a water-borne disease.
Parvin is too poor to have been able to afford a photograph of her son. Now, all she has to remember him by is his death certificate.
A victim of poverty and greed, Parvin's son is one of an estimated 55,000 children who died of water-borne disease in Bangladesh this past year, according to WaterAid, an international group which works to improve access to clean water around the world.
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In Dhaka, slums spring up almost overnight, mostly on illegal landfill that is officially owned by no one. Because there is no owner of record, the Dhaka municipal water company refuses to bring in water pipes -- which means an estimated 5 million slum-dwellers have no legal access to the city water supply.
Enter the black marketers.
We found them in every slum we visited: middlemen who, for a price, sell water they procure from illegal connections to the city water supply. The quality of their water is largely unknown.
The gravelly-voiced middle man who runs Parvin's slum unapologetically shows us his water source: an ancient leaky hose that runs through a ditch filled with raw sewage. This hose supplies the water Parvin must give her remaining children ... the water she will give her new baby after she gives birth. It is the sole source of drinking water for 200 other people in this slum.
"20/20" obtained a water sample from this hose, and tested it for contamination. The water tested positive for E. coli, a potentially deadly bacteria.
The middle man admitted people sometimes got sick from the water. "We can't help it," he said, "because the water is contaminated with sewage."
For adults who have more reserve and may have some immunity, the tainted water is not necessarily fatal. But for young children who have no immunity, and who may be weakened by malnutrition, death can sometimes occur in a matter of hours -- a result of extreme dehydration and loss of electrolytes.
And slum-dwellers like Parvin pay much more than they can afford for this tainted water.
Carel de Rooy, UNICEF representative in Bangladesh, says slum dwellers pay on average 23-times more for their water than the middle class who can get it from the city water utility. "The poorest pay more for water than the better off."
"We collect 60-70 taka per house," the middle man told us -- equivalent to about a dollar.
But make no mistake -- it's big business.
Monir Alam of UNICEF estimates the illicit profits from a single illegal line that runs into Parvin's slum to be 40,000 taka a month -- about $370 -- and there are tens of thousands of these connections in Dhaka's slums.
But where does that water come from?
In another slum, we meet a middleman who is openly collecting money as our cameras roll. When we ask where the water comes from, he says, "Can't say that. You have to ask the boss," although he wouldn't tell us who his boss was.
But Parvin and the families in her slum have been told their illegal water comes direct from the municipal water supply, known as WASA -- in their case, from a local WASA substation just a few hundred yards down the road.
The middleman from Parvin's slum admits the same thing in an interview: "The water commissioner is giving us these two lines, and from these lines everyone gets water. It comes from WASA."
But when we interview the manager of the WASA substation, he professes total ignorance.
"People are going in and putting in the pipes themselves," he protests. "The office isn't doing it. It is 'system loss.'"
"System loss" is the term WASA officials use for the water that gets siphoned off by illegal means. But critics say "system loss" is lining the pockets of corrupt officials all over Dhaka.
Editorials in Dhaka newspapers periodically call for investigations, but according to Carel de Rooy, not much changes.
"The solutions are there -- the question now is to obtain the political will from the government to actually address the slum areas seriously," he said.
Non-government organizations (NGO's) like UNICEF, WaterAid, and DSK have been able to persuade WASA to install legal metered water lines in a small number of Dhaka's 5,000 slums -- cutting out the possibility of corruption, and putting the middlemen in those slums out of business. But widespread implementation of this policy is still a distant dream, according to Shafiqur Rahman of WaterAid. The sale of illegal water is just too lucrative.
According to a 2010 Bangladeshi government report, system loss in Dhaka now stands at a staggering 38 percent of total daily capacity -- in a city that already faces acute water shortages. Last April, government troops were called out to protect WASA stations from public mobs protesting corruption and contaminated water.
And the results of slums without safe water can be deadly. "20/20" interviewed six women who have recently lost children to diarrhea and other waterborne diseases. Five had no choice but to buy illegal water from middlemen and in each case, samples taken from their water sources by "20/20" tested positive for E. coli.
Dr. Steve Luby, a research scientist at the International Center for Diarrheal Disease Research, says that the slums of Bangladesh represent a window into our own future; a future where water becomes a scarce and precious commodity.
"We need to learn as a species," says Dr. Luby, "how we're gonna manage this scarce resource. And in some ways, we ought to think about our groundwater like we think about our oil, because it's more like a nonrenewable resource."
The "Be the Change: Save a Life" initiative is supported in part by the Bill & Melinda Gates Foundation.