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Make Each Drop Count: Harvest Water for the Landscape

Posted 1/16/2008

Written by Susan Donaldson Tuesday, 01 January 2008

When I was a child growing up in New Jersey, my grandfather had a thriving garden filled with fruits and vegetables, even though he lived on a tiny lot in an urban setting. What was the secret of his success? He wasted nothing, including the water running off his roof. Rainwater was captured in barrels for later use to irrigate plants. He was practicing water harvesting, a method of capturing and using rainwater for landscape irrigation or domestic uses.

Water harvesting is an ancient concept; it has been practiced for thousands of years in Asia, India, and the Middle East as a way to supplement water supplies during dry periods. Before municipal water systems existed, people often relied on rainwater to supplement the drinking and irrigation water drawn from rivers or wells. I had an opportunity to see water harvesting in action when I visited Australia last year. South of Adelaide and two hours from the mainland, residents of Kangaroo Island are dependent on rainwater harvesting coupled with the diminishing supplies from a single reservoir to provide all their water needs. Each house, shed, and office building is equipped with a large water tank that captures and stores the roof runoff for later use. Needless to say, I did not see very many lawns during my stay!

With the growth of urban centers complete with municipal water and storm drain systems, many of us have forgotten what my grandfather knew: rain is a high-quality, free source of water that can easily be used for irrigation with minimal effort. The water is soft, low in salts and dissolved minerals, and excellent for leaching our desert soils. However, the water should not be used for drinking purposes unless first purified.

Benefits of Water Harvesting

  • Save money by using “free” water.
  • Reduce the use of treated drinking water for landscape irrigation.
  • Improve plant health by irrigating with high-quality salt-free rainwater.
  • Reduce the potential for moisture damage around your home’s foundation.
  • Keep water out of the municipal storm drain system.
  • Reduce dependence on groundwater supplies.
  • Decrease runoff pollution and protect our rivers and creeks.
  • Reduce flood flows.

To determine if water harvesting will work for you, visualize your property. Where does the water go when it rains? It’s likely that much of the water is conveyed via gutters onto paved surfaces and then into the storm-drain system. This water dumps into ditches and rivers, and is sent downstream rather than soaking into the ground. Worse yet, storm water accumulates pollutants—oil drips, lawn fertilizer, and, this time of year, road salts—that have been deposited on surfaces over which the water flows, and contributes to water pollution.

Instead, consider capturing roof water in a rain barrel or cistern, or diverting your gutter downspouts into landscaped areas or onto your lawn. You might wonder if we receive enough precipitation in Nevada to make capture and use worthwhile. Let’s do the math. In an average year, the Reno area receives about seven and a half inches of precipitation. If your house has a roof area of about 1,500 square feet, and you capture or divert all the water for landscaping purposes, assuming about 90 percent of the water makes it to the tank or planting bed, you will have made use of about 6,300 gallons of water that otherwise would be wasted.

Before you go outside and stick a plastic garbage can under a downspout, there are a few things to consider. First of all, it’s important to know how much water will be delivered to your storage tank at one time. Perhaps you’re only collecting water from one side of your 1,500 square foot roof. When we receive a heavy, 1-inch rainfall, 750 square feet of roof will provide about 420 gallons of water!

In this situation, it will be important to have an overflow mechanism and a plan for the excess water if a small barrel is used.

There are many commercial barrels available. A quick search of the Internet will provide a wide variety of options. You can also construct your own rain barrel using a fifty-five-gallon plastic drum. Retrofit the barrel with a screen at the inlet to exclude debris and insects, and install a spigot to which a hose can be attached. By placing the spigot a few inches above the bottom of the barrel, any debris that does find its way into the system will remain at the bottom. Barrels that are open to the atmosphere can become breeding grounds for mosquitoes, and should be avoided. Instead, seal the lid, and connect the gutter downspout to the lid, sealing any gaps. It’s also important to have a tamper-proof design that does not attract curious children!

Since the water will flow from the barrel under the force of gravity, place it on cinder blocks or a platform elevated at least fifteen inches above the ground. If you would like to capture more rainwater, consider linking two or more barrels together, or placing a barrel at each downspout from your roof. Always design an overflow pipe to allow excess water to safely vent.

Ways to Conserve Water Indoors

  • Don’t let the water run when you brush your teeth.
  • When waiting for water to heat up, capture the cold water and use it to water plants.
  • Install low-flow shower heads and toilets.
  • Add flow reducers to all faucets.
  • Fix leaks immediately.
  • Run the dishwasher and clothes washer only when full. Better yet, replace your old appliances with new Energy Star—certified appliances.
  • Flush the toilet less often. Or, install new “dual flush” toilets that use half the normal amount of water to flush liquid wastes.

Does this sound like too much work? Alternatively, you can simply divert the roof water directly onto your landscaping. There are a variety of low-cost products available that attach to downspouts and divert the water to your plants. First, determine which areas of your landscape will benefit from additional water. In my case, I have a row of lilacs about six feet from my house. Lilacs flourish with a bit of extra water, so I diverted my roof runoff onto the lilacs and an adjacent poplar tree. There is never enough water to result in flooding as my soil is very sandy and porous. If your soils are clayey, or have slow infiltration rates, a rain barrel may be a better choice.

For more information on water harvesting and water quality issues, contact Susan Donaldson, University of Nevada Cooperative Extension, 784-4848 or donaldsons@unce.unr.edu.

Susan Donaldson is the water quality and weed specialist for the western area of University of Nevada Cooperative Extension.

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