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Rainwater Harvesting

Learn about rainwater collection and its benefits

What is Rainwater Harvesting?


Rainwater harvesting is collecting the run-off from a structure or other impervious surface in order to store it for later use. Traditionally, this involves harvesting the rain from a roof. The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel. Rainwater collection systems can be as simple as collecting rain in a rain barrel or as elaborate as harvesting rainwater into large cisterns to supply your entire household demand.

The idea of rainwater harvesting usually conjures up images of an old farm cistern or thoughts of developing countries. The reality is that rainwater harvesting is becoming a viable alternative for supplying our households and businesses with water. It's not just for the farm anymore! There are many countries such as Germany and Australia where rainwater harvesting is a norm. Due to the green building movement, you will be seeing rainwater harvesting systems become more popular here in America.

The collection of rainwater is known by many names throughout the world. It ranges from rainwater collection to rainwater harvesting to rainwater catchment. In addition, terms such as roofwater collection or rooftop water collection is also used in other countries.

We believe that rainwater harvesting is a viable technology in an urban setting. All that is necessary to take advantage of this resource is to capture the free water falling on your roof and direct it to a rainwater storage tank. By doing this, you can take control of your water supply and replace all or at least a substantial portion of your water needs. Rainwater harvesting systems can be configured to supply your whole house and/or your landscape needs.

What are the benefits of rainwater collection?

  • Rainwater is a relatively clean and absolutely free source of water
  • You have total control over your water supply (ideal for cities with water restrictions)
  • It is socially acceptable and environmentally responsible
  • It promotes self-sufficiency and helps conserve water
  • Rainwater is better for landscape plants and gardens because it is not chlorinated
  • It reduces stormwater runoff from homes and businesses
  • It can solve the drainage problems on your property while providing you with free water
  • It uses simple technologies that are inexpensive and easy to maintain
  • It can be used as a main source of water or as a back up source to wells and municipal water
  • The system can be easily retrofitted to an existing structure or built during new home construction
  • System are very flexible and can be modular in nature, allowing expansion, reconfiguration, or relocation, if neccesary
  • It can provide an excellent back-up source of water for emergencies

What are the uses of collected rainwater?

You can essentially use rainwater anywhere you use tap water. The idea of using drinking water to flush our toilets and water our lawns is wasteful and irresponsible, especially in light of population growth and water shortages across the country. Rainwater collection is a technique to green your home and to lessen your environmental footprint.

There are basically three areas where rainwater can be used:

  • Irrigation use
  • Indoor, non-potable use
  • Whole house, potable use

Here are some ideas for specific uses of rainwater:

  • Hand water your lawn and garden
  • Connect rainwater collection system to irrigation/sprinkler system
  • Wash your vehicles
  • Wash your pets
  • Refill your fountains and fish ponds
  • Refill your swimming pool
  • Replace the use of tap water with rainwater to wash your driveways and sidewalks (if you don't use a broom)
  • Use it for all indoor non-potable fixtures (toilets and clothes washer)
  • Use it for all potable needs when properly filtered and disinfected
  • Use it for industrial processes instead of municipally treated water

How much rain can I collect?

The amount of rainfall that you can collect is governed by the following formula:

1" of rain x 1 sq. ft. = 0.623 gallons

Or put in an easy form to remember :

1" of rain from 1,000 sq. ft. will provide 623 gallons

To calculate the amount of rainwater you can collect, you need to know your annual average precipitation for your area. You can use the precipitation map below to find an approximate amount for your area (click for a zoomed image).

United States Annual Average Precipitation Map 1971-2000

Alternatively, you can find an exact precipation amount by looking at the NCDC Monthly Precipitation Probabilities and Quintiles. Find the closest weather station to you and use the 0.5 row to determine your annual average precipitation.

Once you have the annual average rainfall in your area and the square footage of your collection surface, you can plug these values into our rainwater collection calculator.

So you're convinced that rainwater collection is a technology that you want to implement at your house. Next, we will discuss the various methods and components of rainwater harvesting. Even though rainwater catchment is an old technology, there have been many improvements over time through product development.

Go to the next step: How to Collect Rainwater

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