Shower Pumps, are generally required if you already have a mixer shower and are experiencing flow problems due to low pressure in the supply pipe work. A pump can be installed to increase the pressure of stored hot and cold water, not from mains-fed water. For example, Shower Pumps & Pumped Power Showers cannot be used if you have a Combi Boiler or an Unvented Cylinder.
Shower Pumps are available with Single Impellers and Twin Impellers. Impellers are the Inlet and Outlet pipes attached to the pump. If you are looking to boost your hot water supply then a single impeller pump would be required, if however, you wish to boost both your hot and cold water supply, then you would need to install a twin impeller Booster Pump.