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?