Illustration of a module system using a GRP tank.
This type of system differs from the other systems in that they do not replenish the storage tank with mains water. Instead there is an integral mains water cistern which the pump draws from when there is insufficient rainwater in the storage tank. Cistern, pump and controls are assembled into one unit making for easy installation. Module systems usually require a relatively short distance between tank and pump (or suction lift), due to the limitations of suction pumps.
N.B. - In areas with a low mains water flow-rate the pump may deliver water at a higher rate than the integral cistern can be refilled.