THE pollution of Hong Kong waters is notorious, so it is astounding that suppliers of sea water for restaurant fish-tanks should draw water from contaminated areas and that restaurant proprietors do not insist that the water be clean. Self-interest, if not common sense and concern for fellow human beings, should dictate that neither the suppliers nor the proprietors would want to run their risk of poisoning customers. Even more staggering is the delay in taking action after the problem of contamination had been identified scientifically. The Environmental Protection Department has been calling for action to clean up fish-tanks for two years, after analysis of water from the Causeway Bay typhoon shelter had produced alarming results. Now that a case of cholera has been traced to a restaurant fish-tank, the health authorities should be stirred to act. They should certify relatively clean areas as the only ones from which tank water may be drawn and make it an offence to take water from other places. There is also a suggestion that the use of ultra-violet lights to disinfect any polluted water should be made compulsory. If the technique is effective, so it should be. The pollution of the territory's waterways is going to get worse before it gets better. And the incidence of cholera, an often-fatal disease, is rising throughout the region. In the interests of public health, all authorities involved in policing standards of hygiene in restaurants should implement measures to ensure fish-tank water is clean. There is no excuse for dithering when the price of delay might be death.