Harvesting Rainwater

By: Rosemary Stephen PMed, (cert) EOH, IPM, Elements: Environmental Health Intelligence

Potable water is precious as only 1% of the earth’s water is suitable for human consumption [1]. Aquifers are increasingly under threat from unreliable weather patterns brought on by climate change as well as from development, from overpopulation and from deforestation. This means that water must be managed in a sustainable way. One water management method increasingly under consideration is the collection of rainwater. Australia has taken steps to reduce its citizens’ dependency on surface water and aquifers. The government has instituted programs to collect rainwater; new housing developments are now designed with catchment systems that collect rainwater for drinking, cooking and sanitary purposes and the owners of older houses are being encourage to retrofit these systems [2]. This has inspired me to do the same and collect rainwater for my own home use [3, 4].

A word of caution here. Not all roofs can be used to collect rainwater for drinking, cooking and gardening. If the roof has lead paint, tar, acrylic base paint, asphalt, wood shingles or gravel on it, it cannot be used [5, 6]. Rainwater can still be collected by other methods such has building an inverted pyramid suspended over a barrel [7] or adding other rainwater catchment materials to your roof [8, 9] such as corrugated steel sheets, terra-cota roof tiles, UPVC, bamboo or ceramic. If the rainwater is intended for drinking purposes, a filtering system made of woven cotton or a sari material folded at least 4 times could be added to remove unwanted contaminants before the water is collected [10].

Rain barrels are being advertised more and more on the web and in hardware stores. They come in a variety of aesthetically appealing models, usually with a 50 to 60 US gallon capacity. Looking at a typical family of four, how many rain barrels would I need for domestic use and for watering my vegetable garden during the summer?

The first important piece of equipment to own is a rain gauge. This relatively cheap instrument will measure how much rain has fallen and how much rainwater has been collected [11]. A typical 1,000 square foot roof (92.9 square metres) can yield 600 US gallons (2,271.2 litres) of rainwater for every 1 inch (2.5cm) of rainfall [12]. If a typical rain barrel has a capacity of 50 US gallons (189. 25 litres)  it would require 12 rain barrels to harvest that much rainwater [13]. Lack of space can be an issue, especially in small backyards, so there are now companies that specialize in selling high capacity and compact rainwater harvesting systems.

Oak whiskey barrels and barrels made of ordinary plastic can be used to collect water for a garden as long as there is no possibility of chemicals leaching into the water [14, 15]. Food grade plastic barrels are recommended if you are collecting water for drinking and cooking purposes [16]. The catchment source, catchment system and storage tanks must also be protected. Rain barrels must be opaque to prevent the formation of algae while air pollution, bacteria, insects and bird droppings must not enter the water collection system. Diverting the first rain prior to harvesting allows time for the roof to be rinsed which will greatly decrease chances of contamination [17]. Placing screening over the collection barrels is another way to prevent contamination from insects, debris and pollution. Care in the collection process, adequate disinfection methods and regular cleanings can make rainwater safe for drinking and cooking [18]. If contaminates enter the system, it must be cleaned and decontaminated. The Australian government has published a good on-line health guide entitled “Is the water in your rainwater tank safe to drink?”. This guide provides details on what to do if you suspect that your system has become contaminated [19].

How long will 12 barrels of rainwater last? According to the World Health Organization (WHO) the recommended human water intake is 2.5 liters (0.7 US gallon) per person per day [20]. The water used for cooking, washing and bathing averages at 100 litres (26.4 US gallons) of water per person per day or 400 litres (105 US gallons) per day for a family of four [21]. In order to maintain the WHO’s minimum acceptable quality of life, a family of four would use a little bit more than two barrels per day to fill all their water needs, so 12 barrels of water would last about 5 days.

It is harder to predict the amount of water required to water a vegetable garden. This would depend on the size of the garden, the types of plants, the amount of natural rainfall and gardening practices. Best practices such as planting drought resistant crops, mulching, using floating row covers and watering during the coolest parts of the day would greatly extend the use of the collected rainwater [22].

References:

[1] Water Trivia Facts (1995) Office of Water, United States Environmental Protection Agency. (On-line) Available: http://media.mgbg.com/wkrg/photos/weather/downloads/Water_Facts.pdf. Cited 2010 Feb 03.

[2] 7.3 Rainwater, Australia’s guide to environmentally sustainable homes (2008) Technical Manual. (On-line) Available: http://www.yourhome.gov.au/technical/fs73.html. Cited 2010 Feb 18.

[3] An Environmentally Sound Approach for Sustainable Urban Water Management: An Introductory Guide for Decision-Makers (2010) United Nations Environment Programme Division of Technology, Industry and Economics. (On-line) Available: http://www.unep.or.jp/Ietc/Publications/Urban/UrbanEnv-2/index.asp. Cited 2010 Feb 19.

[4] Tapping Into Fog (1998) The International Development Research Centre (IDRC). (On-line) Available: http://www.idrc.ca/en/ev-26965-201-1-DO_TOPIC.html. Cited 2010 Feb 18.

[5] A health Guide to Your Rain Water Tank (2008) Articlesbase. (On-line) Available: http://www.articlesbase.com/bath-showers-articles/a-health-guide-to-your-rain-water-tank-421866.html. Cited 2010 Jan 29.

[6] Rainwater Harvesting (2005) Coalition Fact Sheet, A green Affordable Housing (On-line) Available: http://frontierassoc.net/greenaffordablehousing/FactSheets/GAHCfactsheets/29%20Rainwater%20Harvesting%20final.pdf. Cited 2010 Jan 29.

[7] Staedter, T. Water From Air, Low-Tech Style (2007) Current History, Discovery Channel. (On-line) Available: http://dsc.discovery.com/news/2007/06/15/waterfromair_tec.html?category=history&guid=20070615160030. Cited 2010 Feb 19.

[8] A health Guide to Your Rain Water Tank (2008) Articlesbase. (On-line) Available: http://www.articlesbase.com/bath-showers-articles/a-health-guide-to-your-rain-water-tank-421866.html. Cited 2010 Jan 29.

[9] Rainwater Harvesting (2005) Coalition Fact Sheet, A green Affordable Housing (On-line) Available: http://frontierassoc.net/greenaffordablehousing/FactSheets/GAHCfactsheets/29%20Rainwater%20Harvesting%20final.pdf. Cited 2010 Jan 29.

[10] Moore., D.R. Lecturer. Water Conveyed Poisoning and Diseases in Bangladesh: A Humanitarian Disaster Relief Strategy Through Sustainable Aid (2010) Jha.ac. (On-line) Available: http://www.jha.ac/articles/a130.htm. Cited 2010 Feb 19.

[11] Poole, B. Rainlog.org tells how much rain hit your home (2010) Tucson Citizen. (On-line) Available: http://www.tucsoncitizen.com/daily/frontpage/22279.php. Cited 2010 Jan 29.

[12] Rainwater Harvesting (2005) Coalition Fact Sheet, A green Affordable Housing (On-line) Available: http://frontierassoc.net/greenaffordablehousing/FactSheets/GAHCfactsheets/29%20Rainwater%20Harvesting%20final.pdf. Cited 2010 Jan 29.

[13] Rain Barrels Facts (2008) Aaron’s Rain Barrels & more. On-line) Available: http://www.ne-design.net/rain-barrel-facts.html. Cited 2010 Jan 29.

[14] Oak Wiskey Barrel (2008) Aaron’s Rain Barrels & more. On-line) Available: http://www.ne-design.net/oak-whiskey-barrel.html. Cited 2010 Jan 29.

[15] Audet, M. How to make a rain barrel cheaply (2010) HubOages. (On-line) Available: http://hubpages.com/hub/How-to-Make-a-Rain-Barrel–Cheaply. Cited 2010 Jan 28.

[16] Ibid. Cited 2010 Jan 28.

[17] Is the water in your rainwater tank safe to drink? Environmental health guide. http://www.eastfremantle.wa.gov.au/uploaded/pdf/rain.pdf. Cited 2010 Jan 26.

[18] Ibid. Cited 2010 Jan 26.

[19] Ibid. Cited 2010 Jan 26.

[20] Gleick, P.H., Basic Water Requirements for Human activities: Meeting Basic Needs (1996). (On-line) Available: http://www.emro.who.int/ceha/pdf/Basic.pdf. Cited 2010 Jan 26.

[21] Ibid. Cited 2010 Jan 26.

[22] Efficient Water Use in the Vegetable garden (2010) University of California Cooperative Extension. (On-line) Available: http://cecalaveras.ucdavis.edu/water.htm. Cited 2010 Jan 29.

Tagged as: Water