For many years, the standard for residential domestic hot water systems has been an oil, gas or electric hot water tank that provides a reliable supply of water at a set temperature. The temperature gradient within the tank was thought to be of little importance, as long as the outlet temperature was constant. It was only when Sharp and Loehrke's [36] report on the topic was published in 1979, followed by Hollands and Lightstone [37] ten years later, that the potential benefits of thermal stratification became apparent. Thermal stratification of a hot water tank involves maintaining the temperature in the upper area at a high temperature for use as domestic hot water, while the temperature at the base of the tank is kept at a lower temperature. This allows domestic hot water to be drawn from the upper part of the tank at the required temperature while the water sent through the solar collection system can be drawn from the lower area of ​​the tank at a temperature closer to the ambient temperature, increasing the efficiency of the reservoir. solar thermal collectors [38]. Thermal stratification increases the efficiency of the system by 5 to 15% [36, 37], mainly through a decrease in thermal losses from the storage tank and an increase in the efficiency of the solar collector. The disadvantage of thermal stratification, as will be discussed in this review, is that the cooler region of the stratified reservoirs provides an excellent environment for the growth of Legionella pneumophila. While thermal stratification results in a significant increase in efficiency, an energy efficient method must be implemented to eliminate the resulting risk of Legionella growth to maintain resident safety while maintaining a net increase in system efficiency of domestic hot water. Legionella ...... middle of paper ......and HSE [20], especially when using heat eradication in conjunction with another form of Legionella disinfection. Evans [17,18] suggested thermal eradication methods for single-coil auxiliary preheat solar thermal tanks as well as dual-coil solar thermal tanks with a top electric coil, designed to be energy efficient while maximizing the effect on Legionella cultures. Evans [17] also recommends that, in cases where water above 60°C cannot be pumped to the bottom of storage tanks, another method of systemic disinfection be used in conjunction with thermal eradication. Greenskies Solar Systems [19] added to Evans' work, recommending that hour-long thermal eradication be carried out between 4pm and 5pm. From these reports a clear conclusion can be drawn to minimize the growth of Legionella in thermally stratified solar hot water systems.