Conventional twin coil solar water heating hot water stores are reported by a UK government water safety agency WRAS as being highly likely to be creating a Legionella safety risk. This risk can be minimised by better design. The safer solution used by Solartwin is called dedicated solar volume in time. This safer design involves heating to the base of a hot water store every day in the evening to 60C. This solar hot water storage method fullly complies with UK HSE Legionella guidance para 158. The safety principles also apply to heat pumps. A suggestion of how to calculate the number of people infected wth Legionella per year in UK is given in the video.