A Sourcebook for Green and Sustainable Building

Harvested Rainwater

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Harvested Rainwater Contents:

CSI NUMBERS
DEFINITION
CONSIDERATIONS
COMMERCIAL STATUS
IMPLEMENTATION ISSUES
GUIDELINES

RESOURCES

CSI NUMBERS:

Rainwater harvesting systems are required by law in new construction in Bermuda and the US Virgin Islands. California offers a tax credit for rainwater harvesting systems and financial incentives are offered in cities in Germany and Japan.

DEFINITION:

In this section, Harvested Rainwater is rainwater that is captured from the roofs of buildings on residential property. Harvested rainwater can be used for indoor needs at a residence, irrigation, or both, in whole or in part.

CONSIDERATIONS:

The Austin area receives an average of 32 inches of rain per year. A 2000 square foot area can capture 36,000 gallons of water, which would match up 100 gallons per day in water demand. This is a significant amount of water toward the needs of a water-conserving home.

The quality of rainwater can vary with proximity to highly polluting sources. However, in general, the quality is very good. The softness of rainwater is valued for its cleaning abilities and benign effects on water-using equipment. As an irrigation source, its acidity is helpful in the high PH soils of our region and, as one would expect, is the best water for plants.

Rainwater harvesting systems designed to fill all the water needs of a home can be similar in cost to the expense of putting in a well. Operating costs for a rainwater system can be less. Rainwater collection systems designed to supplement the water needs of a home already on the city system for irrigation purposes can be costly. The primary expense is in the storage tank (cistern). In our area, the cistern size for irrigation can be large due to the high temperatures and extended dry periods in the summer. If the system is not counted upon as the only source of irrigating water, building as large a cistern as one can afford is often the measuring gauge for cistern size.

Commercial
Status		 Implementation
Issues
technology suppliers cost financing public regulatory
Rainwater Harvesting yellow green red yellow green green

Legend
green Satisfactory
yellow Satisfactory in most conditions
red Satisfactory in Limited Conditions
black Unsatisfactory or Difficult

COMMERCIAL STATUS

Technology:

Fairly well-developed; new products are being developed. Rainwater harvesting is an old tradition practiced in all parts of the world including Texas.

SUPPLIERS:

Suitable roof and gutter materials are common products in our region. Specialized products such as roof washers (pre-filters) are also available in our region. Storage tanks (cisterns) are available regionally and statewide. System designers and installers are present locally.

COST:

Rainwater harvesting systems are costly compared to a city hookup. Compared to a well, they are equal or, likely, greater in cost.

IMPLEMENTATION ISSUES

FINANCING:

Appraisers may not properly value a rainwater harvesting system and underwriters may not accept this system as the sole source of household water. If the owner provides a backup water source, such as an on-demand supply contract with a water hauler, lenders would be more favorably inclined to accept such systems. It has become more common for new homes with rainwater systems to receive conventional financing.

PUBLIC ACCEPTANCE:

In the Austin region, there are a small but increasing number of rainwater harvesting systems. A small segment of the population desires rainwater catchment systems for indoor water use. A larger portion of the population feels there is an advantage of using captured rainwater for irrigation. Rainwater harvesting presentations draw large crowds.

REGULATORY:

At present, there is no Texas regulation for rainwater for indoor or outdoor household use unless the system is backed up by publicly supplied waterlines. If a backup system is used, to avoid any cross-connection, an airgap must exist between the public water and rainwater. (An example is a city water line feeding into a rainwater cistern.) This airgap must exceed two diameters of the city line in width. The Health Department will require that the rainwater system does not contribute to mosquito breeding by having an uncovered cistern.

Guidelines

RESOURCES

PROFESSIONAL ASSISTANCE:

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COMPONENTS / MATERIALS / SYSTEMS:

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A variety of galvanized and other tanks are available from farm supply stores. If such tanks are adapted, they must be covered.

GENERAL ASSISTANCE:

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More Information:

NET RESOURCES:

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Sustainable Building Sourcebook web version copyright Sustainable Sources 1994-2008.

This file last updated on Saturday, January 13, 2007