Rainwater harvesting is a technique used for collecting rainwater from rooftops, structures and paved areas. The collected water is Stored in tanks and can be filtered for various applications such as bathing, showering, toilet flushing, pool, laundry and irrigation. If properly filtered and sterilized, rainwater is suitable for potable use.

Rainwater harvesting can save up to 90% of a water bill. Sewage cost is directly related to water consumption, and by reducing the consumption from municipal supply, the sewage cost is also reduced.

A typical rain water harvesting system will consist of:

- Installation of leaf and debris traps on the gutter downpipes, to prevent large solids from entering the rainwater tanks.
- Storage of the water in plastic or steel tanks.
- Filtration of the water to remove fine solids and organic matter.
- Sterilization of the water.
- Feeding the water to the application required (irrigation, household use, potable supply, etc.).

If filtered to SANS241 specifications, the water can be reticulated directly to the municipal mains supply of the house, provided that a suitable backflow preventer is installed to ensure no harvested water is fed back to the municipal supply. An automatic switchover system is installed to switch from rainwater to municipal supply when the rainwater supply is depleted.