Rainwater is water harvested directly from roof runoff from domestic or commercial buildings and captured in rainwater tanks.
Rainwater availability is seasonal. The climate in Perth has large variations in rainfall that is high in winter when watering demand is low and low in summer when demand is high. To optimise the full potential of rainwater as a water source (in Perth) the rainwater system should be plumbed into the building for non-drinking purposes, such as in laundries and toilets.
On average, a roof area of 100 m2 (approximately 50 per cent of an average house in Perth) can collect about 50 000 litres of water a year when plumbed for internal and external use. With an appropriately sized rainwater tank this could supply up to 20 per cent of a household's water needs.
Before installing a rainwater tank, some of the factors to consider include:
- rainfall for the region – seasonal patterns and potential annual yield
- roof catchment size (area of roof discharging to tank)
- roof characteristics (roof material, structures above the roof that may rust or corrode)
- water demand (intended use, in-house and garden)
- tank capacity and available space for tank
- if plumbed into buildings – best location of tank(s) to connect to pipes
- reliability of source for indoor use and required back-up supply
- cost (installation in new developments may be more cost-effective than retrofitting) and regular maintenance
- approval – most local councils require approval of a building application before installation; check with your local council
- a licensed plumber is required to install the tank, fixtures, pipes and pumps
- the local council can provide information on rainwater tank approvals for single houses.
Supply option for large buildings or new urban developments
A considerable volume of rainwater can be collected from the roofs of large residential or commercial buildings within a community, stored in tanks or underground, and distributed through a 'third pipe' scheme to multiple users for non-drinking in-house use and watering of green spaces. A water service provider may be required where roof catchments/tanks are shared and the water is delivered to multiple users. More information for developers is provided in the Department of Health's Draft Alternate Water Supply Guidelines – Stormwater and Rainwater (2009).
The Department of Health provides more information on the safe use of rainwater in urban and regional areas and links to other relevant websites. www.public.health.wa.gov.au/3/659/2/rainwater_collection.pm
The Department of Health has adapted the Australian Guidelines for Water Recycling: Stormwater Harvesting and Reuse (Phase 2) to Western Australian standards. The Draft Alternate Water Supply Guidelines – Stormwater and Rainwater (April 2009) refer to rainwater tanks used for communal water supply and are available on the Department of Health's website.
The Department of Water and Environmental Regulation's information on the benefits and design factors for rainwater tanks and storage.
Water Corporation: List of waterwise plumbers in the Perth metropolitan area and country areas north and south of Perth. http://www.watercorporation.com.au/save-water/find-a-waterwise-specialist
Marsden Jacob Associates:The cost effectiveness of residential rainwater tanks in Perth. A report prepared for Water Corporation and the Department of Water, Perth, Western Australia, 2009.