Rainwater tank
From Wikipedia, the free encyclopedia
   Some of the rainwater tanks around CERES Community Environment Park, in Melbourne, Australia. |
A rainwater tank is a water tank which is used to collect and store rainwater runoff, typically from rooftops.
The stored water can be used for flushing toilets, in washing machines, watering gardens, washing cars, or for drinking.
Rainwater tanks are installed to make use of rain water, reduce mains water use, and aid self-sufficiency. Tanks can also be used for detention of stormwater.
However, the initial upfront cost may be discouraging, especially where water charges are otherwise fixed. Also discouraging may be the maintenance required, or the health risks if maintenance is not carried out.
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[edit] Contamination and manteinence
If water is used for drinking, it is usually filtered first. Filters may remove pathogens which may be present in rainwater (such as cryptosporidium and giardia), or for chemical contamination in some areas. While rain water does not contain chlorine, contamination from airborne pollutants, which settles onto rooftops, may be a risk in urban or industrial areas. Many water suppliers and health authorities, such as the New South Wales Department of Health, do not advise using rainwater for drinking when there is an alternative mains water supply available. However, reports of illness associated with rainwater tanks are relatively infrequent, and public health studies in South Australia (the Australian state with the highest rainwater usage rate) have not identified a correlation. Rainwater is generally regarded as fit to drink if it smells, tastes and looks fine.
Certain paints and roofing materials which may cause contamination. In particular, a Melbourne Water publication advises that lead-based paints never be used. Tar-based coatings are also not recommended, as they affect the taste of the water. Zinc can also be a source of contamination in some paints, as well as galvanised iron or zincalume roofs, particularly when new, should not collect water for potable use. Roofs painted with acrylic paints may have detergents and other chemicals dissolve in the runoff. Runoff from fibrous cement roofs should be discarded for an entire winter, due to leaching of lime. Chemically treated timbers and lead flashing should not be used in roof catchments. Likewise, rainwater should not be collected from parts of the roof incorporating flues from wood burners. Overflows or discharge pipes from roof-mounted appliances such as air-conditioners or hot-water systems should not have their discharge feed into a rainwater tank.
Maintenance includes checking roofs and rain gutters for vegetation and debris, maintaining screens around the tank, and occasionally desludging (removing sediment by draining and cleaning the tank).
[edit] Tanks
Rainwater tanks are constructed from materials such as plastic (polyethylene), concrete, and galvanized steel, as well as fibreglass which is rust and chemical-resistant. Tanks are usually installed above ground, and are usually opaque to prevent the exposure of stored water to sunlight, to avoid algal blooms.
Tanks are also covered and screened to exclude insects, debris, animals and bird droppings. Tanks often come with a plastic inner lining to both increase the life of the tank and protect the water quality.
Apart from rooftops, tanks may also be set up to collect rainwater from concrete patios, driveways and other impervious surfaces.
Sizes typically range in capacity from around 400 to 100,000 litres (approximately 100 to 25,000 gallons). Larger tanks are commonly used where there is no access to a centralised water supply. Also affecting tank size is predicted rainfall and rainfall variability; the higher prices for larger tanks; intended use of rainwater and typical consumption for these uses; the area of roof draining into the tank; security of supply desired.
[edit] Compatibility with centralised water suply
Rain water can be tapped using an electropump.
[edit] See also
- Aljibe.
- Cistern.
- Drinking water.
- Dry land.
- Electropump.
- Rain gutter.
- Hand pump.
- Irrigation tank - ancient India.
- Overflow pipe.
- Plumbing.
- Rainwater harvesting.
- Runoff water.
- Sustainable living.
- Rain barrel.
- Water tank.
- Well.
[edit] External links and references
- Rainwater, Fact Sheet, greenhouse.gov.au
- Rainwater tanks, Choice consumer guide
- Rainwater Tanks (PDF), NSW Health
- WSUD Engineering Procedures: Stormwater. Robin Allison, Matt Francey. 2005 (Melbourne Water). Published by CSIRO Publishing.
