The concept of harvesting rainwater is quite simple: capture – filter – store – distribute. It’s a financially- and environmentally-attractive proposition, since roughly 27% of the domestic mains water we pay for is literally flushed down the toilet. The key for installing successful rainwater harvesting (RWH) systems is in the quality of the components and expert advice at the design stage. Water treatment, storage and distribution technology is continually evolving. The latest devices mean minimal maintenance, long life and very clean water.
The design and components of any system depend on:
- What the water is to be used for
- How rainwater overflow is handled
- Whether storage is above or below ground
- Number of users and volume of water
An office block needs different equipment to a house, but all systems have the same basic elements. They vary in complexity and capacity depending on the scale and requirements of the installation.
A design may specify above ground or below ground tanks depending on the volume of water to be stored and aesthetic factors or planning permission. Above ground tanks can be one-piece or sectional and are often insulated. Underground tanks are usually plastic or fibreglass, though sometimes concrete or steel. 1,500 to 3,000 litres is usually enough for domestic requirements while large commercial systems may need 100,000 litres or more.
Good designs include tank features such as:
- Pre-tank Filters
- Calmed inlet to avoid disturbing sediment on the tank floor
- Overflow unit or trap with a backflow prevention mechanism
An outlet connects to the distribution system for the building, farm, or other application, such as commercial vehicle washing.
The initial filter is the most important component in the system and selecting a good quality one will reap rewards in the long run. The best rainwater filters are virtually non-blocking. This means you don’t need a first flush diverter to discard the first portion of a downpour. There are several types of filter: downpipe, pre-tank and in-tank and some have self-cleaning technology. Additional fine sediment filter and a UV unit can kill pathogens to raise water purity to bathing or even drinking quality.
Storage tanks and filters are the bare bones of a RWH system. Some simple domestic gravity-fed systems with the tank in the roof have little more than those basic components. Larger, more complex systems for bigger buildings may require additional elements.
- Pump and pump controller – underground storage tanks need the water to be pumped to user points, such as toilets, by external or submersible pumps.
- Advanced filtration where there is significant water contamination.
- Monitoring units for storage tank levels, contaminants, water pressure and so on.
- Booster pumps, particulate filters, floating suction filters, mains water backup.
- Header and break tanks for secondary storage.
Find Out More
Download our free Rainwater Harvesting System Guide for more factors to consider when designing a rainwater harvesting system for your application.