Tank ‘top-up’ systems ensure that if levels in the rainwater tank fall to a designated minimum level, mains water (if it is available in the area) is used to 'top-up' the tank with a small volume of water. This minimum water level can be set at any height, however typically will be just above the tank outlet point, so that as much of the tank volume is available for rainwater capture when it rains. This ensures there is always a supply of water in the tank to meet your requirements.

These systems are also called 'trickle-feed' systems and are important when rainwater from the tank is the source of water for internal purposes, such as toilet flushing or laundry use.

The system from Rain Harvesting Pty Ltd utilises WaterMark® approved components, is housed in a unit on top of the tank and is configured to ensure a visible air gap is maintained between the system outlet point and the water level in the tank when it is full to overflowing. This prevents backflow of water from the tank to the mains supply network and potential contamination.