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Rainwater Harvesting

Rainwater harvesting techniques recycle storm water for irrigation.

1,200 gallon rainwater storage tank is buried underground.

High density developments have a big impact on municipal water sources and aquifers. Clean water is becoming a precious commodity in some regions. Here's a simple technology that you should know about that can make a big difference. Rainwater harvesting techniques can provide a free, higher-quality source once the initial investment in collection and storage systems is recouped.

The parts of a complete system include the catchment area (a roof), a rainwater conveyance system (gutters and leaders), holding vessels (cisterns), a roof-wash system (usually the first 10 -20 gallons of rain are diverted from the cistern), a delivery system (pumps) and a treatment system (filters and/or purifiers). Systems can be custom designed and built or purchased as a package. The components may be added by retrofitting existing gutter/leader and roof systems. Uncoated stainless steel or galvanized steel with a baked-enamel finish that is certified as lead-free are considered the best choices for rainwater catchment.

Environmental Performance

By collecting and resusing rainwater, less water is used from the municipal system. As fresh water is a more scarce thing, this system allows people to extend their use of rainwater that is typically absorbed into the ground.

Safety and Disaster Mitigation

These systems can help in times of drought by providing water harvesed during periods of rain. Plants necessary for environmental stability can be watered and, in some setups, fresh drinking water can be created.


The majority of consultants and dealers are in Texas. However, systems have been custom built all over the country. Parts are widely available throughout the U.S. If an old roof is used as the catchment area, if it is under tree branches, if the building relies on wood heat, or if the air is too polluted, you need to be wary of elevated contaminant or toxin levels. Roofs with wood shakes, concrete or clay tiles, or asphalt shingles can support unwanted biological growth, such as mold or bacteria, that will require adequate treatment. Some materials, such as terne coating, lead solder, or treated wood, can leach unwanted toxins.

Calculations to determine the cost-effectiveness are required, and energy consumption for treatment adds to the cost.

The cost varies enormously depending on the chemical qualities of the rain and the roof, and the end use of the water. A complete system (not including the roof) can cost $20,000, albeit with sophisticated filtering and purification components, whereas a system used for watering plants may run only $200.

Not Applicable

Codes and restrictions regarding water supply are not nearly as restrictive as those governing water disposal. In Texas, an airgap must exist between the public water and the rainwater if a backup system is used, like a city water line feeding into a rainwater cistern. The Health Department will insist on a covered cistern, to avoid mosquito breeding. The local building or health department should be contacted prior to installing a rainwater harvesting system.

Chapman Companies: Rancho San Marcos, Santa Fe, New Mexico

The installation effort depends on whether the roof and/or drainage system need to be modified or replaced. Check the composition and condition of the roof and/or drainage system, and the intended use of the water. Drinking water requires a leach-free metal or fiberglass roof and drainage system in addition to filtration or other purifying components. The majority of the components simply bolt-on. A roof-wash system, for instance, is relatively easy to attach to a gutter.

Systems vary by manufacturer and by part. Their warranties range from 1 to 5 years.

Systems are most cost-effective in parts of the country where the water supply is of poor quality, erratic or expensive. In areas not served by a municipal water supply, or in drought-prone areas, installing a rainwater catchment system may actually be the most convenient and economical option. In regions where the municipal water quality is questionable, filtered rainwater can be a sales asset for the home builder. Groundwater is much more vulnerable to environmental contamination than rainwater.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the U.S. Department of Housing and Urban Development (HUD/FHA), The Partnership for Advancing Technology in Housing (PATH), or any PATH-affiliated Federal agency or private company. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.