Bangladesh is currently confronted with what is probably the largest case of mass poisoning in the history of humankind. About one third of her 125 million inhabitants are being slowly poisoned by drinking water that contains arsenic. The consequences have already affected tens of thousands: skin discoloration, ulcers, and cancer of the skin, lungs and intestines. Experts both in Bangladesh and at the World Health Organization (WHO) suspect that nearly 20 million people are, to a greater or lesser extent, already suffering from arsenic poisoning. If non-polluted drinking water supplies are not restored soon, arsenic poisoning might soon be the most frequent cause of death in Bangladesh. EAWAG scientists are presently concentrating on the development of a simple solar arsenic-removal-procedure (SORAS).