W A T E R   F E A T U R E

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Monsoon Harvest

by Janice Austin,
Master Gardener

Desert rainwater is a valuable and unpredictable resource, coming to us free and natural, containing little salt and lots of nitrogen for the first 24 hours after it falls. Southwestern gardeners watch as the scorching skies grow heavy with monsoon moisture, hoping for a welcome bounty over the monotonous, dry summer season. Some of these gardeners are choosing to harvest this scarce and beneficial rainwater, because plants grow better with rainwater than groundwater, with its load of salt and chlorination.


Historically, Southwestern municipalities have hastened to move desert rainwater away from the cities in the quickest ways possible, because of heavy localized rains that have in the past caused extreme flooding; however, there is new thinking regarding rainwater as something to be managed and stored. As the long drought continues, some cities are striving to raise awareness of water use and management, such as the City of Tucson's free downloadable manual on Rainwater Management and Harvesting Principles, available at: http://dot.ci.tucson.az.us/stormwater/education/whm.pdf. There are many ways to improve water use that may benefit all of us.

To begin to do this, start small, in your own backyard. Assess your individual property to determine the site "watershed." Usually rooftops make up the highest elevation of a site, and this elevation is considered the top of the watershed, the best place to collect rainwater. The most practical way to do this is by installing rain gutters, along with something in which to collect it, moving it into rain barrels or cisterns.

Good assessment and planning also help prevent flooding on your property, as will incorporating water management features, such as berms, swales, basins, French drains, or gabions, into your landscape. Note that rainwater coming off an asphalt roof will not be suitable for drinking water, nor for leafy vegetables, though it can be used for watering woody plants, which remove any toxins from the asphalt. But, really, how much rainwater can there be in the desert? Why bother to collect it at all?

Let's take a closer look. To calculate the runoff from a roof, measure the footprint of your dwelling drip line‹Width x Length. Roughly, it is possible to collect 600 gallons of water per inch of rain falling on 1,000 square feet of collection surface. On average, the Phoenix area receives approximately 7 inches of rain annually. That is a lot of water when it falls in heavy, localized monsoon rains, if left unmanaged and flowing into the streets. By putting up rain gutters, it can help keep that beneficial bounty at work on your property, benefiting your plants, and in turn, help reduce street flooding in your neighborhood.


The task of putting up rain gutters is not what it used to be, back in the days of working with sharp-edged, cumbersome aluminum gutters. Now, for just a little more money at your local major home improvement center, you have the option of choosing vinyl rain gutters, which are surprisingly easy to install. In addition, vinyl rain gutters never require painting and have a limited lifetime warranty. Although aluminum gutters are cheaper to buy, in the long run they also require more time for caulking and special tools for installation. The only tools needed for vinyl gutters are safety glasses, measuring tape, pencil, level, chalk line, saw, and a drill and screwdriver set. Their simple vinyl components of gutters, joiners, hooks and end caps snap together like children's "Tinker Toys." (See photo)

Begin by sketching your total layout. To put up a rain gutter, carefully measure the length of each gutter run and determine the best drop outlets at points that will allow for drainage away from the building foundation. Take your time in planning. Remember that one drop outlet is required for every 40' of gutter. Additional downspouts increase handling capacity, whether into additional rain barrels or landscape features. At the high end of the run, drive a nail _" below the top of the fascia board. Snap a "level" chalk line from this nail to the opposite end of the gutter run. Drop the chalk line 1/8" for every 10 feet of gutter and snap your "guide" line. Cut the measured gutters straight, using a cutting guide, if necessary. Don't rush and work safely. Then, assemble the gutters on the ground, slipping the various components and cut gutters together, according to your measured plans. Hold up the first gutter section along your "guide" line, and begin fastening it from the middle of each section with 1" screws. No caulking is required, as it snaps together with a leak-proof seal into the hooks, joiners, and end caps. Continue with the process, until done. You may also opt to slip in leaf guards onto the tops of the gutters, to keep out leaves and debris.

The real highlight of the rain gutter construction process is the trial run, when a bucket of water is hoisted aloft and poured into the high end of the gutter, to see how it runs its course for the first time. If you prefer to not tackle this project, either aluminum or vinyl gutters can be installed for you at your location. There are many creative ways you can choose to make use of the coming monsoon harvest, and these can benefit you, your plants and your property for a long, long time.

Photo and Illustration: Janice Austin.


Maricopa County Master Gardener Volunteer Information
Last Updated November 2, 2004
Author: Lucy K. Bradley, Extension Agent Urban Horticulture, University of Arizona Cooperative Extension, Maricopa County
© 1997 The University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension in Maricopa County
Comments to Maricopa-hort@ag.arizona.edu 4341 E. Broadway Road, Phoenix, AZ 85040,
Voice: (602) 470-8086 ext. 301, Fax (602) 470-8092