Saving the Rain

Saving the Rain

  • By David K Garth
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  • March 2016-Vol.2 No.3
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Saving rainwater for gardening may be an idea whose time has come.  Whether you think California’s endemic droughts are an anomaly or the harbinger of things to come, even a short-term lack of water for residential gardeners can be serious.  It makes the difference between flowers with colors that pop, vegetables with natural sweetness, green lawns that spring under your feet versus a brown, droopy landscape canceling out all your hard work.  Water is indeed the elixir of life.

Although many plants can endure dry periods, there are critical stages in development that require water.  The germination of seeds begins with a steady supply of moisture, not too much and not too little, in order to break down the seed coat and feed the delicate embryo.  If bedding plants are set out in the garden, daily watering for the first few days helps roots take hold. Some vegetables have specific needs as they near fruiting.  Diane Relf points out that “corn needs water at two crucial times: when the tassels at the top are beginning to show, and when the silk is beginning to show on the ear. If weather is dry at these times, water.” “June Tips: Vegetables”  It’s water that swells the fruit and aids the color in our blossoms.  Availability of water at these particular times is necessary for good results.

Storing and making use of rainwater not only saves money and helps the environment by reducing wasted runoff, it also offers significant benefit to plants with a supply of relatively clean, soft water.  Saving the water than comes from the sky begins with conservation in the broadest sense and adds value to the effort we put into making things grow.  In order to set up your own rainwater harvest, you need to consider collection, storage and delivery systems.

Collection.  Our gardens suffer when rain is either stingy or overly generous.  A downpour can cause erosion that removes valuable topsoil.  Run-off in urban areas washes pollutants into streams and overtaxes storm water drains.  On the other hand, extended dry spells starve plants and may result in wells going dry or restrictions on the use of public water supplies.  The easiest collection method for most of us involves capturing the rainwater that comes off your roof.  Depending on the size of your roof, even a gentle shower can produce hundreds of gallons.   Instead of going into the neighborhood drains and ditches, the water you save can be gradually added in the garden, also supplementing groundwater.

Before going further with collection schemes, consider these practical questions:

First, how much water do you want or need to have available for the growing season?  This will depend on the size of your garden and the average rainfall in your area.

Second, how much can you conveniently store?  The storage options range from a modest barrel tastefully tucked into a corner and extend all the way to an underground cistern.

Third, are there legal restrictions, zoning regulations, or courtesies to be considered? While I’m not aware of municipalities in central Virginia restricting rainwater-harvesting — as we find happening in some western states — neighborhood covenants about appearance may apply to your situation.

The simplest system places a barrel directly under a downspout.  If you line up several barrels, PVC pipes can connect one or several downspouts into a central supply line to collect water and carry it to the first barrel.  Pieces of hose will take overflow from the first barrel to a second and so on.  Calculating the footprint of your house in square feet will give a rough estimate of the amount of water coming through your system.  Use the following rule: one inch of rainfall on a 1000 square foot house produces approximately 600 gallons.  That’s a lot of H2O.

Water from the gutters goes underground to a 2400 gallon cistern. Photo: David Garth

Water from the gutters goes underground to a
2400 gallon cistern.
Photo: David Garth

Roofing materials make a difference.  In fact, some roofing materials are toxic.  Wooden shingles treated with chromated copper arsenate render rainwater from those roofs unusable for the garden. Zinc antimoss strips have the same deleterious effect.

Asphalt shingles tend to accumulate bird droppings and particulate matter, but those pollutants are usually washed away with the initial runoff.   You’ll want some sort of screen to catch larger trash such as leaves.  In addition, if you want to control that initial runoff pollution, you may want to look at a couple devices on the market that allow diversion of that “first flush.”  A list of products is located at the end of the article by the Brooklyn Botanic Garden at   Or you might want to simply create your own “first flush diverter” using a standpipe.  If you’re handy, you might be inspired by the detailed photos and drawings of such diverters at oregonstate/rainwaterharvesting.

Metal roofing will have fewer pollutants than asphalt shingles, and these more limited pollutants can be diverted with the same “first flush” devices described above.

The article “Rainwater Harvesting for Gardening Use” is actually a spiffy slideshow well worth a look.  It’s worth a detailed look.

Except for the prohibition on rainwater from chemically treated roofing, scientific tests of rain barrel water in New Jersey indicate that “overall the water quality of the rain barrel water [is] very good.”  Still the researchers at Rutgers concluded that —

[e]ven though a low percentage of samples exceeded the irrigation limits, caution is still warranted when using harvested water to water a vegetable/herb garden to reduce the risk of exposure to a harmful contaminant like E. coli.

The Rutgers scientists suggest that homeowners who do not have a “first flush” diverter, should clean and treat their rain barrels with small amounts of bleach —  about 1 oz. of household bleach per month.   For more details on these recommendations and the research upon which they are based, see “Rain Barrels Part IV: Testing and Applying Harvested Water to Irrigate a Vegetable Garden,” at

Storage. It turns out that large food-grade barrels, usually made of a plastic material and holding 40-80 gallons, are often available to the public for little or no cost.  Similar commercial barrels can be purchased for appearance and convenience.   My barrels pictured once held soft drink components.  A brown barrel is produced commercially for gardeners.  Remember that water is heavy.  At 8 pounds per gallon, a 50 gallon barrel weighs 400 pounds; so plan the foundation and placement of these items carefully.  Do not attempt to use containers that once held petroleum products or harsh chemicals since they are too difficult to clean.


 A plastic tank collects water from a downspout for use in a courtyard. Photo: David Garth

A plastic tank collects water from a
downspout for use in a courtyard.
Photo: David Garth

One advantage of plastic is that holes can be drilled easily to securely fit a piece of hose near the top to carry the overflow and to attach a spigot near the bottom.  Remember to leave enough space and height to fill a watering can or bucket.  Locating the storage container just a foot or two higher than the garden allows you to utilize gravity to carry water to your plants by means of a hose.

Periodic maintenance for your system can be lessened if the containers are opaque, in order to discourage algae growth, vented but screened, to reduce odors and mosquitoes, and cleanable since some dirt will find a way inside.

A larger and more elaborate storage facility utilizing a tank would service a larger garden and prepare for longer dry spells.  Such tanks can be made from concrete and buried in the ground much like a septic system, or fabricated from metal or fiberglass.  A simple pump and hydrant system will deliver water under pressure.

istern water is pumped to a hydrant beside the garden. Photo: David Garth

Cistern water is pumped to a hydrant
beside the garden.
Photo: David Garth

Delivery.  As the previous section implies, bringing water to your plants can be as straightforward as turning on the spigot to fill a watering can or as complicated as setting a timer to start pumping water through an irrigation system.  Every situation is a little different and every gardener will have to think about his or her own preferences within the limits of their situation.  The following quotation sums up the value of careful planning for a useful system:

It isn’t easy to come up with “one size fits all” instructions for building rainwater harvesting systems because of variations in styles of roofs, downspouts, storage tanks, and garden layouts. You have to use a combination of research, common sense, ingenuity, and dumb luck to design and build your system.

Lenny Librizzi, “Gardening with Rainwater”

Maintenance.  In addition to keeping your gutters running clear of leaves and branches, the screens that keep out smaller particulate matter need to be cleaned.  Annual inspection of storage units will insure efficient use of vents and overflow outlets as well as preventing mosquito breeding.  The advantages for our pocketbooks and our environment as well as our gardens make the effort worthwhile.


Detailed instructions for making a rain barrel can be found at “How to Harvest Rainwater,”,

“Rainwater Harvesting for Gardening,” Oregon State Extension,

“Rain Barrels, Part IV:  Testing and Applying Harvested Water to Irrigate a Vegetable Garden,” Rutgers Coop. Ext. (New Jersey Agricultural Experiment Station, 2013).

“Household Water Conservation,” (offers more reasons for saving rainwater).

“Plant Propagation from Seed,” Diane Relf,

“Rainwater Harvesting,” David J. Sample,, ( this article has a useful bibliography).

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