A Better Rainwater-Harvesting System

Think beyond the rain barrel: This simpler, cheaper approach to rainwater harvesting will help you harvest much more water for your garden!

| August/September 2012

Rainwater Harvesting System Illustration

This simple rainwater-harvesting system will put the water where your plants need it most.


Harvesting rainwater to use for growing vegetables makes a great deal of sense. Unfortunately, the most common method of rainwater harvesting isn’t the most effective. Typically, gardeners invest in a rain barrel — which holds only 50 or 60 gallons of water — and then dole out the captured water to plants as needed, hopefully emptying the barrel before the next storm.

But 50 gallons is only a small fraction of the water you could be harvesting each time it rains. During a 1-inch shower, more than 900 gallons of water flow off the roof of a 30-by-50-foot house or barn. Instead of catching just a little bit of it in a rain barrel, why not capture it all? You can do just that with a simple setup that diverts rain from your downspouts directly to your garden. We’ll tell you more about how to do this in a minute, but first, we’ll explain why we think it’s such a good idea.

How Soil Stores Water

Even many experienced gardeners have trouble comprehending just how much water soil can hold. Except in areas with consistently high rainfall, your garden soil’s moisture level will seldom be at “field capacity.” That’s the term scientists use to describe the maximum amount of water a soil can hold. When it rains or when we irrigate, gravity pulls the water down into the soil. After a heavy rain, some of the water may move all the way down to the water table or the bedrock, but a large amount of it is held by capillary forces that cause water to coat each soil particle and partially fill the spaces between particles. (An example of capillary action is the way a paper towel absorbs liquid.) That capillary water is what your crops use as they grow.

Each soil’s field capacity varies depending on how much sand or clay is in it. One cubic inch of coarse sand may contain 125,000 particles, while the same amount of the finest silt could contain 15.6 trillion particles! Soil particles have an astonishing amount of surface area. One cubic inch of an ordinary soil (with a mix of sand, silt and clay particles) could have a surface area of 25 square feet.

What those numbers mean is that many soils can hold 2 to 3 inches of water in each foot of soil depth, and garden soils that contain lots of organic matter can hold even more. Crop roots can reach down 4 feet — sometimes even 8 feet deep — to tap this capillary water. To be sure crops get the water they need, gardeners would ideally want to keep their soil moisture near field capacity to a depth of at least 4 feet. During peak growth, crop transpiration together with surface evaporation can draw as much as a half-inch of water per day. The more water you’ve stored in your soil, the less you will need to provide supplemental irrigation.

To understand how soil moisture levels vary in your area, check out the soil moisture maps from the National Weather Service. These maps will tell you whether soil moisture levels in your region are above or below normal at any particular time.

5/29/2015 10:48:10 PM

The harvesting of water in this way, not only saves work but money and natural resources that can be put to use to the advantage of all in order to produce more food and at the same time possibly saving a lot of dirt erosion. I will definitely give this a try, and pass on the knowledge I have just received, and AM anxious to have the opportunity to obtain more. Thank you very much for such wonderful knowledge.

1/5/2015 11:00:06 AM

should read:....... harvest, BUT can......

1/5/2015 10:57:08 AM

I don't have a tip for rain water harvest, nut can I suggest another way to harvest water form what you already pay for? 1. We have a pvc pie that goes from our washing machine to our garden so we catch the rinse water from each load. The only thing to remember is not to use bleach,vinegar, or soda in your wash. The free and clear or homemade detergents work best;plus help deter pests. 2.We took our bath tub off the main and ran another pvc pipe out to a barrel system to catch the water there.It works great! The trade is that I already paid for the water AND I get to continue to use the water with less of a bill for gardening.

12/27/2014 2:44:09 PM

I wish I had a gutter close enough, but we also don't get enough water here in Idaho. I do have a rain barrel plus I have a sprinkler head in my garden space that I have attached a large irrigation line to. I then run drip lines off of that. It waters my whole garden, including my black and raspberries. My tomato plants grow bigger than I know what to do with.

3/28/2014 11:45:01 AM

I was also worried about roof runoff water quality, this pdf from North Carolina Extension helped. http://www.bae.ncsu.edu/stormwater/PublicationFiles/RooftopRunoff2009.pdf Great idea and will be trying this

9/13/2013 5:23:38 AM

Really interesting read, never learnt about soil and its properties! http://www.cotterillcivils.co.uk/products/rainwater-harvesting.aspx is booming right now! We to get the rest of the world doing such!

9/13/2013 5:23:19 AM

Really interesting read, never learnt about soil and its properties! http://www.cotterillcivils.co.uk/products/rainwater-harvesting.aspx is booming right now! We to get the rest of the world doing such!

Hans Quistorff
2/1/2013 2:43:25 AM

I have a corrugated plastic-fiberglass roof on my greenhouse. the gutter feeds a 6 foot by 2 foot deep stock tank on a three foot high stand. I can use the hose from the tank to water the plants in the green house then use the quick connect to the drip distribution in my raspberry tunnel. It takes about 24 hours to empty the tank with three rows of weeping hose 100 feet long.

tony rutt
1/31/2013 8:39:54 PM

Cheryl, you and Mother Earth News readers may be very interested to learn about the Rainwater Hub, an entirely new way of collecting and distributing rainwater. The rainwater hub can be found at, surprise, surprise, www.rainwaterhub.com ! Thanks!

Michael Porter
1/30/2013 5:16:20 PM

I do not like the small bucket idea knowing volume and pressure of forced water during a storm, I would bet the buckets would over flow first before enough water filled the hoses and drip lines. I use multiple rain barrels and use the same concept except I have stored water for drought times. When it rains why add more water to the area, the pressure alone from water would just run off and be wasted in the cities water system. When you water containers you just don't dump water on the plant and walk away, you give enough to make the soil wet and come back and water again and allow time for absorption. The soils speed of absorption is the questionable component.

11/8/2012 8:09:55 AM

I'm surprise there is no caution about the type of roofing material. Here in Seattle city has published a guide stating that you should NOT use rainwater to water edibles if the roof is composed of wood shingles or shake treatd chromtaed copper arsenate. Copper roofs and gutters and zince galvanized metal should not be used. Asphalr roofs and flat tar roofs leach complex hydrocarbons. If your roof has been treatd with anti moss, kichen or algae kilinfg chemicals do not use rainwater. Rainwater from enamled steel and glazed tile are okay to use.

Joan Vibert
8/24/2012 5:10:21 PM

This is a great idea - very simple. However, I would caution folks to know the soil around their homes before planting edible plants. Prior to our purchase, our old farmhouse had been treated for termites using chlordane, a systemic pesticide that the plants will uptake and retain. Since we chose not to ingest this pesticide, we never plant edible around our house. Chlordane is a long-lasting chemical in soil and I wouldn't trust that it would ever just "wash out".

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