BILL BAINBRIDGE, REPORTER: Hanoi is a busy city and it's getting busier. Its population of 6.5 million is growing by more than 400,000 every year; people who need clean drinking water. Much of that water is pumped from underground aquifers, but with demand surging, more and more water is being drawn from deep underground. And it's this water that contains naturally high concentrations of the deadly poison arsenic.
PHAM HUNG VIET, HANOI UNIVERSITY OF SCIENCE: The people for sure, they use this water for the cooking and drinking purpose. So that is why the arsenic concentration in the human body of the people are elevated.
BILL BAINBRIDGE: Now a team of Vietnamese and international scientists has confirmed something that's been long suspected. The research, published in the journal Nature, demonstrates that a clean aquifer can become contaminated as water suppliers accelerate their flows of ground water which contains high levels of arsenic. And while the decade-long study concentrated on Van Phuc, a small village on the outskirts of Hanoi, it has frightening implications for the entire region.
PHAM HUNG VIET: We observe in this village, it can be considered as a natural phenomenon of arsenic contamination in the whole area of the Red River delta generally. And as you know, the Red River delta can be considered as one of the most dense population areas in the world, with about 17 million to 20 million people living in this area. We believe that a big part of this population area can be affected by this.
BILL BAINBRIDGE: And those effects can be severe. Even in low concentrations, if arsenic is ingested over a long period of time, it causes cancers of the skin, lungs, bladder and kidneys. The most visible symptoms are disfiguring skin lesions. In the past, high water levels in the aquifer meant water from these wells was generally safe. But as more ground water has been pumped, water from arsenic-rich sediment is increasingly intruding into the previously uncontaminated water. Pumping for municipal water supplies doubled between 2000 and 2010. Michael Berg is an environmental scientist currently visiting Curtin University in Western Australia.
MICHAEL BERG, SWISS FED. INSTITUTE OF AQUATIC SCIENCE AND TECHNOLOGY: Hanoi, they pump around 1 million cubic metres per day for drink water purposes. And of course this is very large-scale pumping and the groundwater table is drawn down significantly and then of course, water is then towards these production wells.
BILL BAINBRIDGE: That means once-clean wells are now posing a long-term health risk to the people of Van Phuc.
FEMALE VAN PHUC RESIDENT (translation): My family has been using water from a drilled well for over 20 years. Everyone in the village uses it because we don't have other options.
MALE VAN PHUC RESIDENT (translation): I know the water is contaminated, but we have no other choice. We just try to filter the water as much as possible.
BILL BAINBRIDGE: Where arsenic is present, it's at potentially deadly levels. World Health Organisation guidelines for arsenic in drinking water are for 10 micrograms per litre. Concentrations in Van Phuc are 10 to 300 times higher than that.
MICHAEL BERG: It's a very slow disease. So if you're exposed to arsenic, the first year you kind of feel nothing. Then later you may be a little bit fatigued. Then the first symptoms are changes of the skin. You get skin problems, and then various forms of internal cancer. So it's a very slow disease and it's very difficult to diagnose even for professionals.
BILL BAINBRIDGE: One 2008 UN study found as many as 1.7 million people living along the Mekong could be at risk of arsenic poisoning. Authorities in Hanoi have moved to filter arsenic from the city's water supply. But many people on the city's outskirts remain off the water grid. And with rapid urbanisation across the region, the study's authors say it's critical that water infrastructure keeps pace with Asia's booming population.
MICHAEL BERG: Action is required immediately. But as I've said, it's difficult because these are private wells. It's the own kind of initiative of the people to pump this water. More centralised water treatment facilities should be promoted in the villages and then distributed through a pipe system.
MALE VAN PHUC RESIDENT (translation): The city promised that 80 per cent of the population would have access to clean water in 2010. But it is now 2013, and we're still waiting.
BILL BAINBRIDGE: In the meantime, the villagers of Van Phuc have little choice but to drink from their poisoned wells.