How to reduce the risk of legionella contamination in Domestic Hot Water systems

Despite a lot of attention and measures to prevent legionella in residential and commercial buildings such as hotels and hospitals, periodically a new outbreak with sometimes fatal outcome reaches the news. According The World Health Organization a lack of appropriate methods to diagnosing the infection or sufficient surveillance systems, the exact rate of occurrence is unknown. In Europe, Australian and the USA there are 10-15 cases detected per million population, per year.