Rainwater tank: Difference between revisions
No edit summary |
|||
| (4 intermediate revisions by the same user not shown) | |||
| Line 29: | Line 29: | ||
Sizes typically range in capacity from around 400 to 100,000 litres (approximately 100 to 25,000 [[gallon]]s). 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. |
Sizes typically range in capacity from around 400 to 100,000 litres (approximately 100 to 25,000 [[gallon]]s). 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. |
||
==Rainwater tanks as a water supply augmentation option== |
|||
In a broader sense, in urbanised areas of developed countries, where climate change has threatened long-term water security and reduced rainfall over catchment areas, the role of rainwater tanks has come under scrutiny. In many cities, for example, mandatory installation of rainwater tanks to supplement drinking water supplies, has been suggested as an alternative to other water supply options, such as recycling or seawater desalination. |
|||
Tanks are often perceived to have environmental costs that are comparatively lower than other water supply augmentation options for large highly urbanised cities. These must be taken into account when governments implement water security or augmentation plans. Importantly though, options such as seawater desalination emerge as a superior option over consumption of rainwater tank water, when the environmental, economic and social costs are taken into account. Often, arguments in favour of rainwater tanks appear to be ideologically driven, but not justified by economic or environmental analysis. |
|||
Moreover, reuse of rainwater, through stormwater harvesting and mandatory installation of rainwater harvesting systems in properties, is clearly inferior from an environmental and public health point of view. Arguments in favour of stormwater/rainwater harvesting are often simplistic and based on "ideal world scenarios". They are demonstrably weakened, however, when the very high risk of contamination of these supplies is taken into account. Chemical and biological contamination of rainwater storage in highly urbanised cities has led many water authorities or public health authorities around the world to warn of the risks and advise against the consumption of rainwater. |
|||
Economically, rainwater and stormwater harvesting schemes, ranging from tanks to large and complex concrete storages, are considered prohibitively expensive compared to all others, and are best implemented on smaller scales within new development areas. Mandating the installation of rainwater tanks also raises important public policy issues questions regarding social equity, whether the cost of the installation is funded by the individual or the community as a whole, with adverse impacts on economically disadvantaged in either scenario. Critically, removal of large quantities of stormwater from the environment via collection systems, also damages ecosystems due to the reduction in flow of run-off to natural creeks and streams, and ultimately water bodies, in urban areas. |
|||
The importance of local creeks, steams and waterways in urban areas that rely upon stormwater runoff, their flow-on benefits to flora and fauna, and the cleansing effect of stormwater runoff, demonstrate that the old adage of the water that is "wasted down the drains every time it rains" is somewhat of an urban myth. Such factors are being increasingly taken into account in the sensible development of public policy regarding options such as seawater desalination. Such factors have influenced cities such as London, where desalination is now considered a viable water supply option to supplement the water supply of the greater metropolitan region of the city. |
|||
== Compatibility with centralised water supply == |
== Compatibility with centralised water supply == |
||
Revision as of 13:53, 22 May 2007
   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, although consumption of rainwater in highly developed urban areas is frequently advised against.
Rainwater tanks are installed to make use of rain water, reduce mains water use, and aid self-sufficiency. Tanks can also be used for retention of stormwater.
Disadvantages of a rainwater tank include the initial upfront cost, especially where water charges are otherwise fixed. Also the occasional maintenance required, or the health risks if maintenance is not carried out.[1]
Contamination and maintenance
If rainwater is used for drinking, it is often filtered first. Filtration (such as reverse osmosis or ultrafiltration) 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 fit to drink if it smells, tastes and looks fine[2]; However some pathogens, chemical contamination and sub-micron suspended metal may produce neither smell, taste and not be visible to the eye.[citation needed]
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 of algae and other contaminants).
Tanks
Rainwater tanks may be 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 have screen inlets 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.
Rainwater tanks as a water supply augmentation option
In a broader sense, in urbanised areas of developed countries, where climate change has threatened long-term water security and reduced rainfall over catchment areas, the role of rainwater tanks has come under scrutiny. In many cities, for example, mandatory installation of rainwater tanks to supplement drinking water supplies, has been suggested as an alternative to other water supply options, such as recycling or seawater desalination.
Tanks are often perceived to have environmental costs that are comparatively lower than other water supply augmentation options for large highly urbanised cities. These must be taken into account when governments implement water security or augmentation plans. Importantly though, options such as seawater desalination emerge as a superior option over consumption of rainwater tank water, when the environmental, economic and social costs are taken into account. Often, arguments in favour of rainwater tanks appear to be ideologically driven, but not justified by economic or environmental analysis.
Moreover, reuse of rainwater, through stormwater harvesting and mandatory installation of rainwater harvesting systems in properties, is clearly inferior from an environmental and public health point of view. Arguments in favour of stormwater/rainwater harvesting are often simplistic and based on "ideal world scenarios". They are demonstrably weakened, however, when the very high risk of contamination of these supplies is taken into account. Chemical and biological contamination of rainwater storage in highly urbanised cities has led many water authorities or public health authorities around the world to warn of the risks and advise against the consumption of rainwater.
Economically, rainwater and stormwater harvesting schemes, ranging from tanks to large and complex concrete storages, are considered prohibitively expensive compared to all others, and are best implemented on smaller scales within new development areas. Mandating the installation of rainwater tanks also raises important public policy issues questions regarding social equity, whether the cost of the installation is funded by the individual or the community as a whole, with adverse impacts on economically disadvantaged in either scenario. Critically, removal of large quantities of stormwater from the environment via collection systems, also damages ecosystems due to the reduction in flow of run-off to natural creeks and streams, and ultimately water bodies, in urban areas.
The importance of local creeks, steams and waterways in urban areas that rely upon stormwater runoff, their flow-on benefits to flora and fauna, and the cleansing effect of stormwater runoff, demonstrate that the old adage of the water that is "wasted down the drains every time it rains" is somewhat of an urban myth. Such factors are being increasingly taken into account in the sensible development of public policy regarding options such as seawater desalination. Such factors have influenced cities such as London, where desalination is now considered a viable water supply option to supplement the water supply of the greater metropolitan region of the city.
Compatibility with centralised water supply
Rain water can be tapped using an electropump.
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
External links and references
- ^ "Rainwater, Fact Sheet". greenhouse.gov.au: Your Home Technical Manual. Retrieved 2007-02-17.
- ^ "Buying guide: Rainwater tanks". CHOICE magazine. Retrieved 2007-02-10.
- Rainwater Tanks (PDF), NSW Health
- WSUD Engineering Procedures: Stormwater. Robin Allison, Matt Francey. 2005 (Melbourne Water). Published by CSIRO Publishing.
- Water Storage: Tanks, Cisterns, Aquifers, and Ponds For Domestic Supply, Fire and Emergency Use- Includes How to Make Ferrocement Water Tanks Book by Art Ludwig
- Standard Methods for the Examination of Water and Wastewater (standardmethods.org)