Interest in minimising the risk of Legionella in cooling tower water has grown steadily in building management circles and today is one of the most important targets for management. To minimise Legionella, various tools and methods involving chemicals, ultraviolet (UV) rays, etc., have been proposed and are being utilised. Field tests were conducted at 17 sites with the application of four chemicals, two UV-ray devices, four electromagnetic methods, and controls. The test towers selected were inhabited by Legionella. During the course of the tests, comparative and serial observations were incorporated to examine the behaviour of Legionella. As a result, the effectiveness of four anti-Legionella chemicals was ascertained. The effect of UV irradiation was limited. Other physical methods and common agents showed moderate effectiveness. General aspects of cooling water management were also clarified. These results can be directly applied by building management staff in practical operations.

KEYWORDS: site testing, bacteria, legionnaires disease, cooling towers, behaviour, sterilising, chemical cleaning, ultraviolet radiation, maintenance, comparing