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Water Your Garden for Free This Summer

Timothy Boyer Ph.D.'s picture
How to collect rainwater for gardening.

Here’s some useful info with significant money-saving potential by using simple supplies to build your own system for collecting spring rainwater so that you can water your garden for free this summer.


There’s a childhood story that I vaguely recall every time spring and fall rains arrive and flood our area. It’s about these foolish monkeys who spent their time playing and having a good time whenever the sun shone and the skies were blue. But when the rains came, they huddled and shivered with cold, vowing to be prepared next time. But once the sun came out, their vows were forgotten as their thoughts turned to play. Until, of course, the next time the rains returned.

It’s a twist on the old ant and the grasshopper parable, but still effective as a reminder that human nature being what it is, we are all guilty of procrastination at some point or other. With me, it’s making sure the basement sump pump is ready for another rainy season. And, I’ve been lucky so far.

That said, the rains are also a reminder that I am squandering an excellent opportunity to save money with my gardening: saving rainwater for this summer’s garden. I already have invested in a no-till gardening method. And, my plots were pre-mulched with biodegradable leaf bags and straw. Therefore, I have prepared my gardens for a significantly lower usage of water already. But just think, how much greater my savings would be if I could only collect and store all that free rainwater that is coming down today?!

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How Much Money Could be Saved?

According to the EPA, the average household uses about 300 gallons of water per day with about 70% of that going to indoor use and the remainder outdoors. That 300 gallons per day translates into roughly a $70 per month water bill; or, for normal outdoor water use such as car washing, some plant and lawn watering and overall leakage loss, again roughly about $23 per month. Thereby, this then comes to nearly say $280 per year on water used outside the house.

However, you are not the average household: you have a garden or two to boot. According to the Oregon State University Extension Service, garden watering is estimated to require about 2 inches of depth per week. And, that most sprinkler systems have approximately a 75% efficiency in getting the water to the plants.

Therefore, if you have an 8-foot by 4-foot garden plot (32 square feet), you can expect to use roughly 50 gallons of water per week over a 4-month growing season. This is a rough estimate, but not too far removed when compared to an estimation from the Oregon State University Extension Service that it takes about 900,240 gallons of water to sustain a field of crops covering just one acre over a period of 3 months.

Back to your 32 square foot garden plot, it’s going to add roughly $200 more in just water alone toward your final end-of-season garden costs by the time you put produce on your plate. Not insignificant. And that’s only with one plot.

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The other upside to this savings is that you are also helping the environment and gaining other benefits you would not receive by strictly going to the tap.

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Benefits of Collecting Rainwater

According to an Oregon State University Extension Service pamphlet, collecting rainwater offers a number of benefits:

• Harvested and stored rainwater can cut city and well-water consumption by providing an alternative source for irrigating landscapes, vegetables, or small fruit gardens.

• Other than the initial cost of installing a catchment and pumping-and-delivery system, rainwater is free.

• Rainwater also tends to be pure, soft (fewer salts than city or well water), and near neutral pH (not acidic or basic).

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• Capturing, storing, and using rainwater also helps reduce the intensity and flow of storm waters.

• If used to irrigate, rainwater helps flush salts off lawn and garden soils while reducing overall water bills.

Rainwater Harvesting System Components

To install a rainwater harvesting system you will need the following components:

Catchment surface—For most purposes we are talking about your roof that catches the rainfall, and directs the rainfall to your gutters. As it turns out, if your roof is asphalt or composite-shingled, the water quality is good enough for gardening purposes, but not recommended for drinking. However, if your roof consists of wood shingles, tar, gravel, or is a concrete surface, the captured water should only be used for lawn irrigation purposes—not for vegetable gardening. The Extension Service warns that contaminants from these surfaces may not be fully metabolized before being taken up by vegetables.

Gutters and downspouts—While you technically could just collect water directly from your roof’s gutters and downspouts, it’s not a good idea or practice. Bird droppings and other biologic contaminants cover a roof and are typically the first items to be flushed down the gutter along with the collected rainfall. It’s a safer practice to invest in leaf screens and first-flush diverters to provide relatively cleaner water for storage.

Leaf screens—Think of leaf screens as the nose hairs of the gutter system. Leaf screens not only capture a lot of debris that you will not want in your collected water, but also help prevent blockage of the cisterns that will eventually need to be drained by gravity or a pump to deliver the water to the garden.

First flush diverter— A first flush diverter is a “must-have” for any rain collection system. The job of the first flush diverter is to route the first flow of water from the downspout away from the storage tank. This first flush diverter gives the system a chance to rid itself of the smaller contaminants, such as dust, pollen, and bird and rodent feces. Kind of like rinsing food scraps off of your plates before putting them into the dishwasher. After the first cleaning flush has passed, the continued rainfall is redirected to the storage tanks for collection.

Storage tanks (or cisterns)— Storage tanks will probably be the most expensive component to add to your existing home. The Oregon State Extension service notes that the most easily available and affordable storage tank solutions for homeowners are 50- or 75-gallon, food-grade barrels.

Caveats toward selecting your cistern type include:

• should not have previously been used to store toxic materials
• be opaque to sunlight to inhibit algae growth
• be covered and have vents screened to discourage infestation by insects and frogs
• be accessible for cleaning and/or repair
• be close to the irrigation site
• have an inlet that is lower than the lowest downspout exit point
• be placed as high as practicable to reduce load on pump (if using pumps)
• have an overflow outlet directed away from the house foundation or septic drainfields
• be placed on a stable foundation, as water is heavy at 8 pounds per gallon (a full 3,000-gallon tank will weigh over 24,000 pounds)

Delivery system—There are two primary types of water delivery systems from the cistern: gravity fed and pump fed. A gravity powered delivery system is dependent on the storage tank’s elevation relative to the garden. However, a pump system may be more beneficial, especially if you are using some sort of powered drip irrigation device to closely control the watering and thereby reduce waste or loss of water. In addition to the delivery system, for both types you will need a final filtration component to prevent clogging by fine grade contaminants that have made it into the cistern.

For a more detailed discussion and illustrations of what it takes to collect rainwater for gardening purposes, follow the link in the references section below to the Oregon State University Extension Service publication.

If you currently use a rainwater collecting system, send us a description and show us yours photos on how well it works for you.

Timothy Boyer has a Ph.D. in Molecular and Cellular Biology from the University of Arizona. For 20+ years he has been employed as a freelance health and science writer. Today, with a background in farming and an avid home gardener, Timothy continues writing about science with a focus on the connection between plant biology and gardening for healthy living. For continual updates about plants and health, you can also follow Timothy on Twitter at TimBoyerWrites.

Images courtesy of Pixabay


Harvesting Rainwater for Use in the Garden” Oregon State University Extension Service, Dec. 2014 & 2018 by Sam Angima.

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