If 30 inches of rainfall a year is 816,000 gallons per acre, the equivalent falling on an area of 1000 square feet would be 15,000. Thats the average square footage of the roof area in a typical family home (based on a 25 foot x 40 foot suburban roof). When one considers that, for many this valuable resource runs straight off the roof, down the drainpipe, and flows off the property into city sewers and drainage systems.
What a waste of such a valuable resource! Whether simply a landowner, or avid gardener, water is a valuable resource, to be considered in any garden design plan. Capturing and storing water for re-use, as well as introducing methods in the garden to slow the flow of water and reduce the amount lost into the drainage systems is a relatively easy task. As individuals, it is our responsibility, for the community, and even the planet to make small changes, where possible, to respect and extend this valuable commodity.
The easiest way to store water is in the soil and in plants. This may seem absurd, but by increasing the organic matter in the soil, as well as developing good soil structure, the soil can begin to work with the garden, holding valuable water for longer. This in turn acts as a sieve, which allows water to sink through the soil, filtering as it goes, and providing nutrient rich water for the plants in your garden. Creating a rain garden helps to slow down this water flow, allowing it to sink into the garden rather than running off your property and into the city sewers.
This beautiful little guide in Garden Gate Magazine illustrates how to make your own rain water harvester. There's money literally falling from the skies every time it rains. Here's how you can harvest your share.
Creating a rainwater collecting and storage system is simple. (We'll show you where to buy barrels and how to build your own.) And every time you use it to replace expensive, chemically treated city water in your garden, you're saving money.
Best of all, this collection system is right over your head. The three elements of any rainwater harvester are the collection area, the transportation system and the storage facility.
Determining how much water your roof collects can involve lots of complex calculations. But all you really need to do is figure how much water your garden will need and if your roof can collect that much. The gardener who's going to irrigate a large vegetable patch in the desert Southwest will need a lot more water than the one dousing a few container plants on a patio in the Midwest.
The rule of thumb is the average 25 foot by 40 foot home roof sheds about 600 gallons of water in an hour of moderate rainfall, around 1 inch. If you have two downspouts, they'll each divert about 300 gallons of water toward the barrel under them. The more barrels you have, the more of this water you can collect. The gutters and downspouts along the edges of your roof are the water transportation system of your rainwater harvester.
The gutters and downspouts along the edges of your roof are the water transportation system of your rainwater harvester.
Material — Gutters and downspouts can be made from aluminum or plastic. It's the size, not the material that's important.
Size — Gutters and downspouts have to be large enough to carry the water running off the roof. Most home gutters come 5 or 6 inches wide. 3-inch-diameter downspouts attach to the 5-inch gutters; 4-inch downspouts go on 6-inch gutters.
For roof collection areas up to 1000 square feet, a 5-inch gutter and 3-inch downspout are large enough to carry the water. Larger roofs' collection areas should have the larger size gutters and downspouts.
Filters — Be sure there are some kind of screens, such as the one in the illustration, to keep leaves and other debris from clogging the downspouts. In areas where mosquitos are a problem, use a fine-mesh, aluminum window screen to keep the insects away from the standing water in the barrel.
Now we come to the heart of the rainwater harvesting system: Storing the rainwater you collect for use in dry times.
Barrels — There are several great water storage barrels available from specialty garden online catalogs.
Or you can build your own using Garden Gate's plan for constructing a rain barrel.
Placement — Whether you make barrels or buy them, they need to be placed properly.
Locate barrels under a downspout that's also close to the thirstiest parts of your garden.
Dig out a 4-inch-deep area the length and width of the cinder block base. Fill the area with 1/4-inch pea gravel. This makes a base to help you level the cinder blocks and drain away water to keep your foundation dry.
The higher you can raise the barrels, the better the water pressure will be. Raising the barrels up also gets the spigot higher off the ground so you can get a watering can under it.
Capacity — Of course, you can only store the total gallons of water your rain barrels hold times the number of them you have.
Still, the system in the illustration, using three, standard 55-gallon drums, has 165 gallons of water ready and waiting to give the garden a drink when other supplies might not be available.
The more water you can store, the better. Short lengths of hose can be attached to individual barrels to link them together and boost the capacity of your system. And they can be added over time as you see how much water your garden needs.
Overflow — During heavy rains, there may be some overflow from the barrels. The 4-inch layer of gravel under the cinder blocks, as in the illustration, will divert this water away from your foundation. Or you can install an overflow port near the top of the barrel and attach a hose to divert excess water out to the garden.
An excellent online resource for DIY water harvesting projects and examples can be found at build it solar.