Rainwater tank

From Wikipedia, the free encyclopedia


Some of the rainwater tanks around CERES Community Environment Park, in Melbourne, Australia.
Water Portal

A rainwater tank (sometimes called rain barrels, in North America or a water butt in the UK) is a water tank which is used to collect and store rain water runoff, typically from rooftops via rain gutters. Rainwater tanks are devices for collecting and maintaining harvested rain.

Rainwater tanks are installed to make use of soft rain water for home use, reduce mains water use, and aid self-sufficiency. In arid climates, rain barrels are often used to store water during the rainy season for use during dryer periods. Tanks can also be used for retention of stormwater for release at a later time.

Stored water is used for flushing toilets, in washing machines, watering gardens, washing cars, agriculture, and sometimes for drinking, if adequate care is taken that the water is not contaminated.

Disadvantages of a rainwater tank used for drinking water include the initial upfront cost, especially where water charges are otherwise fixed. Occasional maintenance to the tank is also required, or the user runs a health risk if maintenance is not carried out.[1] However, many homes use small scale rain barrels to harvest minute quantities of water for landscaping/gardening applications rather than a potable water surrogate. These small rain barrels, often recycled from food storage and transport barrels or, in some cases, whiskey and wine aging barrels, are often inexpensive. While most are properly engineered to screen out mosquitoes, the lack of proper filtering or closed loop systems may create breeding grounds for larvae.

Widespread use of rain barrels also changes the amount of rainwater reaching the ground in a particular area and draining into streams. Depending on the climate, this either helps prevent erosion, sedimentation, and/or pollution, and can reduce the strain on stormwater drainage systems; or it could cause rivers to dry up and ponds to stagnate if the water is diverted to a different watershed. If collected water is used in the same watershed in which it is collected, rainwater collection actually can stabilize flow in rivers and provide more regular and filtered groundwater transfer into ponds.

Contents

[edit] 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[citation needed] (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 considered fit to drink if it smells, tastes and looks fine[2]; However some pathogens, chemical contamination and sub-micrometre 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 galvanized iron[citation needed] 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).

Rainwater tanks which are not properly sealed (secured at the top) may act as breeding grounds for mosquitoes.[3]

[edit] Tanks

Large polyethylene rainwater tanks being installed underground.
Large polyethylene rainwater tanks being installed underground.

Rainwater tanks may be constructed from materials such as plastic (polyethylene), concrete, galvanized steel, as well as fibreglass and stainless steel which are 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. Almost all steel tanks currently produced for household rainwater collection come with a plastic inner lining to increase the life of the tank, prevent leaks 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 (100 to 25,000 US gallons). Smaller tanks, such as the plastic 208-liter (55-gallon barrel) are used in some cases. 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] Water supply augmentation

In some cities, installation of rainwater tanks may be mandatory, or may help a new building be approved. For example, in Victoria, Australia new houses which have rainwater tank connected to all flush toilets are given an additional 1-star of the required 5-star House Energy Rating. Some governments subsidise purchases of rainwater tanks or provide rebates in areas where they are considered an important means of water supply augmentation.[4]

Rainwater to supplement drinking water supplies may be seen 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. Where stormwater feeds natural creeks and streams, there are concerns about rainwater harvesting systems reducing the amount of run-off entering natural bodies of water.[citation needed]

Rainwater collection can be made compatible with centralised water supply by tapping it using an electropump.

[edit] Colorado law

In the State of Colorado, USA, the installation of rainwater collection barrels is an offense[5]. This is a consequence of the system of water rights in the state; the movement and holding of rainwater is inextricably linked with ownership of water rights and is enshrined in the constitution of the State of Colorado. The use of water in Colorado and other western states is governed by what is known as the prior appropriation doctrine. This system of water allocation controls who uses how much water, the types of uses allowed, and when those waters can be used. This is often referred to as the priority system or "first in time, first in right." Since all water arriving in Colorado has been allocated to "senior water right holders" since the 1850s, rainwater prevented from running downstream may not be available to its rightful owner.

[edit] Calculating rainwater collection

Rainwater collection from roofs can be calculated using the following formulas:

  • 1 inch of rain on a 1000 square feet roof yields 623 gallons of water; or
  • 1 millimeter of rain on a 1 square meter surface yields 1 litre of water.

[edit] Internal rainwater tank

Cape Schank House in Victoria, Australia uses an internal rainwater tank to provide cooling to the living room in summer. During winter the tank is drained and wrapped in an insulating jacket. The tank also provides structural support to the roof, and excess water is used for domestic use including drinking.[6][7]

[edit] See also

[edit] References

  1. ^ Rainwater, Fact Sheet. greenhouse.gov.au: Your Home Technical Manual. Retrieved on 2007-02-17.
  2. ^ Buying guide: Rainwater tanks. CHOICE magazine. Retrieved on 2007-02-10.
  3. ^ The Sunday Age. November 25, 2007. "These flies! Will mozzies be next?". Stephen Cauchi quoting Luke Simpkin, Museum Victoria.
  4. ^ Energy efficiency for Victoria, action plan (pdf). Retrieved on 2007-05-22.
  5. ^ Water harvesting in Colorado (pdf). Retrieved on 2007-08-30.
  6. ^ materialicious » Blog Archive » cape schanck house, paul morgan architects
  7. ^ architecture.com.au - The Royal Australian Institute of Architects (RAIA), architecture, architects, design, australia

[edit] External links

[edit] Building water barrels and tanks

[edit] Initiatives