What size water tank do you need with a 118L cylinder?

minimum size of the cold water storage cistern should be 100litres but a smaller cistern (tank) will work as long as the supply (from cold main) matches the flow (all hot taps on) therefore maintainiing a reasonable level in the cwsc. So in theory you might get away with a much smaller cistern but it must be tested to prove it meets the above criteria, failure to do so could mean that the hot water storage cylinder becomes half empty or worse and the heating elements from either the immersion heater or coil (from boiler) become exposed to air (basically not heating water!) which could damage these components!!