What size cold water tank and hot water cylinder do I need to supply a Satellites digital shower?

The minimum size cold water tank (cistern) we recommend for one shower unit is 115 litres (25 gallons). Hot water storage will depend on a number of factors such as, time in the shower, flow rate of the shower and the stored water temperature and recovery time of the hot water cylinder. As a rule of thumb a digital shower delivering a flow rate of 16l/m will use around 11 litres of hot water a minute. Therefore, this will use up the contents of a domestic hot water storage cylinder containing 117 litres of which 93 litres is useable, in approximately 8 minutes. The larger the hot water cylinder the better.