Houseplans Blog

Rainwater Harvesting

Rainwater Harvesting
Check out this age-old practice.
Rainwater harvesting is an age-old practice that can supply your outdoor irrigation needs while reducing storm water runoff and reducing the demand for treated water. A 1,000 square-foot roof produces about 600 gallons of runoff for each inch of rain. You can estimate your annual water production by multiplying your square footage by the annual rainfall in your area. A water catchment system designed to meet your irrigation needs is easy to build. A system designed to supply potable water for your house is a bit more complicated and involves filtration, pumping and purification. In between are systems that supply irrigation needs outside and toilet and laundry needs inside. The example above is with Plan 935-13.

An outdoor irrigation system can be as simple as a rain barrel hooked up to your gutter system and a hose to direct the water to your plants. A well-designed system starts with a screen that prevents debris from entering the water supply. A first flush diverter is next (image below courtesy Park-usa-com).

The first rain of the year is the dirtiest as it cleans the roof; this plumbing fixture directs the initial water falling on your roof into the drain system. After the diverter 
float reaches the top, the balance of the water is directed into your storage tank. You can then distribute water as needed throughout the year (image below courtesy

To store the water, barrels should be made of an opaque material that inhibits algae and bacterial growth.  Plastic, metal or wood all work well. Some people love the look of a redwood tank similar to the ones found on old -fashioned train stations. Screens on downspouts are next and these along with tight fitting barrel tops

help prevent mosquito breeding. A good source of rainwater storage products, like the sampling shown here, is the website

To distribute water, locate your storage container uphill from your garden or fruit trees. A gravity fed system delivers an average of 5 psi. A drip system requires more pressure and a way to filter the water. Use a pressure sensitive pump and a micron filter to keep the system clean. For household use, you’ll need a way to get the water from the cistern to a supplemental tank located at the top of your house. If you intend the water for drinking and cooking, you’ll also need a filtration system and a way to purify the water. UV purification is the preferred system and eliminates up to 99.99% of bacteria and other contaminants. While whole house systems are not cheap, a small outdoor irrigation system can cost as little as a few hundred dollars. A larger system that covers all of your household needs including filtering and purification can cost upwards of $15,000 or 

more. For helpful information on the wide range of rainwater harvesting products and procedures, visit (image above courtesy Rainbank). Other good information sources are Earthcraft Landscape Design, a company that specializes in the design of rainwater harvesting systems, and ARCSA, the American Rainwater Catchment Systems Association.

A well functioning system requires periodic maintenance. Gutters and downspouts need to be kept free of leaves and debris. First flush water needs draining from time to time and if water is used as drinking water, occasional testing is required to ensure consistent quality is maintained.

Check Regulations
State laws regarding rainwater catchment vary from state to state and even from municipality to municipality. Some states, such as Virginia, are encouraging rainwater catchment and have established the Alternative Water Supply Assistance Fund, providing income tax credit to individuals and corporations installing rainwater harvesting systems. While other states such as Colorado are more concerned with historically established water rights and only allow catchment systems with a maximum capacity of 110 gallons per household.  It is best to check your own state laws regarding rainwater harvesting before investing in a system. A water catchment system is a great way to bring your home and garden more in concert with nature and a great way to reduce your water and energy needs.

Now what about roofs that can provide the runoff? Metal roofs make especially good conduits for rainwater,

as you can see in Plan 479-11, above, by Peter Brachvogel and Stella Carosso, and Plan 454-14 by Sarah Susanka and Tina Govan, below.

For a collection of house plans that includes a variety of designs with metal roofs click here.

Rainwater Harvesting Inspiration

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