“Certified arsenic-free”. The traveller, new to Bangladesh and taking out a bottle of drinking water with this strange label from their hotel fridge, may smile in puzzlement. “Oh well, that’s all right then.” But unless they are keen readers of specialist journals on geology and water engineering, the chances are this is their first inkling of what the World Health Organisation has described as the “largest mass poisoning of a population in history”. Dhaka, the heaving, ramshackle capital of 17 million people, is spreading its concrete tentacles ever outwards across the flat riverine plains of the Bay of Bengal in this country squeezed between India and Myanmar. There’s an in-your-face vibrancy about Dhaka, a smiling