Rainwater Harvesting

What System is Right for Me?


Domestic rainwater harvesting systems are typically classified as either ‘wet’ systems or ‘dry’ systems. 

Dry Systems

In 'dry' systems, rainwater from your gutters is diverted directly into the rainwater tank via gravity flows. These systems are classified as dry systems because the collection network (ie. downpipes) will empty and ‘dry out’ between rainfall events. Dry rainwater systems can use either above-ground or below-ground storage tanks. 

Above-ground (or free-standing) systems commonly only capture flows from between 1 - 3 downpipes nearest to the location of the tank. These systems are the simplest and often the cheapest to install, however, because they only capture rainwater from a few downpipes, they are best suited to low consumption applications - such as toilet flushing, laundries and even as an alternate source of drinking water.  

Underground rainwater tanks are also classified as ‘dry’ system as the downpipes will drain completely when it has stopped raining. 

Wet Systems

‘Wet’ rainwater systems are typically designed to capture all rainwater falling on the roof of a house. All downpipes around the house are connected below ground via a ring main which carries water to the tank. 

These systems maximise rainwater harvesting volumes.

Switching Devices and Pumps

Switching devices commonly use pressure switches and/or floats to automatically detect when sufficient rainwater is available for use in the house. When rainwater levels are low, these devices will automatically change back to mains water so there is an uninterupted supply of water to the house. When levels in the raintank as sufficient, rainwater will be used in preference to mains water.

A pump is an essential component of rainwater harvesting systems - as they are required to provide pressurised rainwater to the house. Rainwater pumping systems can be either above-ground or submersible (located inside the tank). Submersible pumps are slightly more expensive to install than above ground pumps, however have the added advantage of being practically silent when operating. 

Storage Tanks

Rainwater tanks are available in a range of shapes, storage capacities and materials. Domestic systems are typically between 3,000L - 5,000L. These tanks and are often made of polypropylene or corrugated iron. Larger storage volumes can be achieved by linking tanks in series, or by installing underground tanks or even bladder tanks.  


© urban ecological 2016