A home food garden is an excellent resource to reduce household expenses and improve the health and nutrition of the family. There has been a recent increase in food gardening in the United States and in 2008, 31% of U.S. households had a food garden. In 2009, the median size of food gardens in the United States was 96 ft2, the average size was 600 ft2, and 75% of home gardens were at least 400 ft2 (National Gardening Association, 2009). Vegetables are 80%–95% water and therefore their yield and quality suffer very quickly from drought (Sanders, 1993; Straw, 2009). In many regions of the United States, supplemental irrigation is recommended to optimize vegetable crop yield. In the United States, outdoor water use, including food gardens, is about 30% on average of total residential potable water use (Vickers, 2001).
Rainwater harvesting is an ancient technique enjoying a revival in popularity because of the inherent quality of rainwater and the interest in reducing consumption of potable water (Krishna, 2005). Parts of Australia and the southwestern United States have embraced rainwater harvesting as a serious way to augment sparse and irregular water supplies (Lancaster, 2010). In Chicago, during the period 2004–07, 3000 rain barrels were distributed for free to homeowners (Ando and Freitas, 2011).
A catchment area for the collection of rainwater can be any area that collects or sheds rainwater. A roof is the most common and easily accessible area to use for rainwater collection; it uses gravity to direct the water. Most homes are equipped with a guttering system that can easily be adapted to funnel water to a storage tank. For general calculations, ≈0.5 gal of water per square foot of roof area can be collected and stored during a 1-inch rainfall. Some rainfall evaporates from the roof or leaks from the gutters, so an overall efficiency of 80% to 85% is often used in the calculation of harvested water. A rainfall event of ≈0.5 inch will easily fill a 50 to 55-gal barrel; planter beds, vegetable or flower gardens, and potted plants can easily be irrigated with the water from a rain barrel (Watson, 2010). Water is either pumped or allowed to flow by gravity to a nearby garden or landscaped area (P. Gibson, personal communication).
Many reports about the potential of rainwater harvesting use annual or seasonal rainfall and take into account only the size of the catchment area and efficiency of the guttering system (harvest efficiency). However, there are many other factors that should be considered to better estimate the amount of harvested water and associated cost savings. These factors include the size of the garden, length of a dry spell that would trigger use of rainwater from the barrel, and how much water is in the barrel before the homeowner decides to use it. Most of these factors involve day-to-day decisions by the homeowner, and support the use of a model based on daily data. Taking these factors into consideration will help the extension agent or other consultant to provide a more realistic cost-benefit analysis of a typical rain barrel.
The objective of this study was to develop a spreadsheet-based model based on daily weather data in Excel® (Microsoft Corp., Redmond, WA) to determine how the watering habits of home gardeners affect the amount of available supplemental irrigation water and cost savings using a typical 55-gal rain barrel.
AndoA.W.FreitasL.P.C.2011Consumer demand for green stormwater management technology in an urban setting: The case of Chicago rain barrelsWater Resources Res.47W12501
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LancasterB.2010Rainwater harvesting for drylands and beyond. 5 Sept. 2013. <http://www.harvestingrainwater.com/rainwater-harvesting-inforesources/>
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SandersD.C.1993Vegetable crop irrigation. 9 Sept. 2013. <http://www.ces.ncsu.edu/hil/hil-33-e.html>
Southern Region Climate Center2013Climate information for management and operational decisions (CLIMOD). 7 June 2012. <http://climod.srcc.lsu.edu>
StrawR.A.2009Irrigating the home garden. 29 Sept. 2013. <http://pubs.ext.vt.edu/426/426-322/426-322.html>
VickersA.2001Handbook of water use and conservation. WaterPlow Press Amherst MA
WatsonG.2010Rain barrels: A homeowner’s guide. 7 June 2013. <http://www.swfwmd.state.fl.us/publications/files/rain_barrels_guide.pdf>