A century of exploitation of groundwater supplies has drawn down water tables across Vietnam, making it difficult to avoid water contaminated with arsenic even at deeper depths, according to a new study. In tests of 512 private wells reaching depths of 10 to 50 meters (33 to 164 feet), researchers found that 27 percent contained arsenic levels exceeding World Health Organization health standards, putting 3 million people at risk. In the region around densely-populated Hanoi, it has become difficult to tap water that is not contaminated no matter how far down drills reach, according to the study published in the journal Nature. According to researchers, it may be likely that the toxic element could become common in deep aquifers across South Asia, posing significant health risks and economic costs associated with water purification. Exposure to arsenic can trigger numerous conditions, from lesions, to anemia to cancer.