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Experts offer rainwater harvesting hints

February 21, 2008

Media Contacts:
Mitch Woodward, N.C. Cooperative Extension area specialized agent for environmental education, Wake County, 919.250.1112 or;
Dr. Garry Grabow, assistant professor and N.C. Cooperative Extension specialist; College of Agriculture and Life Sciences, North Carolina State University, 919.513.7348 or

Given a situation in which water is an ever-diminishing resource, some people might consider harvesting the free water that falls, upon occasion, from the sky.

Water-harvesting concepts are ancient, dating to the first time humans realized rainwater was caught in depressions in rocks, then learned to make containers to catch the water as it fell.

Today's technology has improved upon those concepts, and catching rain is coming back into style.

Researchers call one such technology "rainwater harvesting," which means capturing stormwater runoff from a roof in a cistern to use in place of a city or well-water supply.

If you're thinking about buying a rain barrel or installing a cistern, North Carolina Cooperative Extension and North Carolina State University experts can offer a few hints.

Mitch Woodward, Cooperative Extension area specialized agent for environmental education in Wake County has a few suggestions.

"I figure it costs about $1 per gallon storage capacity to buy and install a cistern or rain barrel system," says Woodward, who uses data from research by Dr. Bill Hunt, assistant professor and Cooperative Extension specialist at N.C. State University.

"It takes a lot of water to irrigate," says Dr. Garry Grabow, assistant professor and Cooperative Extension specialist at N.C. State and a licensed professional engineer. "To apply 1 inch of water to 1,000 square feet of turf requires 623 gallons. So 'fully functional' cistern systems are expensive, which is why most have been installed at government or other institutional places that have money."

Here are a few things Woodward and Grabow say you should consider if you're thinking about installing rain barrels or a cistern.

1) Will my homeowners association or local government allow it? Some neighbors don't want the tanks visible and some installations of larger systems may violate HOA covenants, Woodward notes. Also, it is important to check with your local public utilities department to ensure that you will not be subjected to any penalties for using harvested rainwater during periods of mandatory water restrictions, Grabow says.

2) Pressure? Most people would like the water to be pressurized. This requires pumps and electricity, and even the best do-it-yourselfers may need to hire a plumber and electrician.

3) Should I choose a cistern or a rain barrel? Both barrels and cisterns capture rainwater, but a barrel's smaller size greatly limits its practicality to watering a few shrubs or flowers when compared with a rainwater harvesting system. Most rain barrel volumes are exceeded during even small rainfall events and only provide enough storage for casual uses.

4) Size? Bigger is better. Most people with rain barrels would like to step up to a larger size.

5)How can I use harvested rainwater?
- Crop irrigation
- Water for gardening
- Vehicle washing
- Toilet flushing
- Clothes washing
- Drinking water (with special treatment)

6)What are the benefits of rainwater harvesting?
- Runoff volume reduction
- Reduction in pollutant load
- Monetary savings on water use
- Reduced demand on water supplies

7) Are there any limitations?
Because a rainwater harvesting system depends on rainfall to recharge, a backup water supply may be required for some applications. Water must be treated for many home uses such as drinking water and washing dishes. You will need a separate plumbing network to keep harvested rainwater from mixing with city or well water.

8) How can I improve the appearance of the cistern?
A cistern can be virtually invisible when installed underground. Cisterns can also be constructed from a variety of materials, including plastic, metal and wood.

9) How much water could I actually save?
N.C. State University engineers have developed a computer model to assist in determining the appropriate cistern size for a given situation. The model is available on line at You can also use a garden water meter, available from many online retailers for around $10, to monitor your current water usage for tasks that could be supplied by a water harvesting system.

10) Can I use harvested rainwater to irrigate during mandatory water restrictions?
Because irrigation with a rainwater harvesting system does not rely upon municipal water sources, it may be exempt from mandatory water restrictions.

More information, including cistern specs, is available online at or on pages 5-7 of an N.C. Cooperative Extension publication titled Urban Waterways that is online at

Written by: Art Latham, 919.513.3117 or

Posted by Dave at February 21, 2008 08:00 AM