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These developments have culminated in the creation of rainwater harvesting provisions in nationwide codes and specifications like the International Green Construction Code (IgCC) and LEED. These developments stand to further drive rainwater harvesting into mainstream use. The challenge for these new efforts will be to fully integrate these systems into modern buildings in such a way as to protect life, health, and safety while delivering the high level of performance and reliability expected of modern water supply systems.


While the concept of rainwater harvesting is fairly simple, there are a number of details that must be managed for rainwater harvesting systems to be used successfully and safely. These are addressed in documents like the ARCSA Rainwater Catchment Design and Installation Standard and the ICC International Green Construction Code, Chapter 7. They include:


• Back flow Protection: All Rainwater Harvesting Systems, connected to potable water supplies must protect these potable supplies with an approved back flow protection devices, such as an air gap or reduced pressure zone (RPZ) back flow valve. This is critical to ensure that potable water supplies are not contaminated.


• Algae Suppression: Without proper design measures, algae growth in rainwater tanks can become a serious problem and impact water quality and performance. Shading the water in tanks from sunlight by the use of opaque materials, shading, or burying can minimize the growth of algae.


• Mosquitoes and Vermin: People are not the only creatures who like rainwater. The presence of stored water creates an ideal home for mosquitoes, rats, frogs, snakes and the like. Systems must be designed to exclude them without sacrificing performance.


• First-Flush Diversion: Collection surfaces (like roofs) are generally fairly clean, but the highest concentration of contaminants are found in the first few gallons of rainwater coming from a given rain event. To cut down on these contaminants, first flush diverters (aka roof washers) divert and dispose of a given volume of water at the beginning of collection. After diversion, the cleaner water from the roof is sent to the tank for storage (and possibly filtration and disinfection). The type and size of diverter varies by application and location, and the ARCSA document provides guidance to a designer.


• Filtration and Disinfection: Depending on where the system is located, what you plan to do with the rainwater, roofing materials, and local laws, you may or may not need to disinfect the collected water. Basic filtration in the form of something called a debris excluder is recommended for most systems to keep out leaves, twigs, and the occasional tennis ball. Beyond that, it depends. Options for disinfection include UV light, ozone, chlorine, and hydrogen peroxide. But, as many rainwater advocates point out, rainwater is very clean, and can be used for many applications without treatment or significant limits on storage time.


• Tanks: Cisterns were a common feature in the past at homes and farms, but today’s buildings are unlikely to have tanks for water storage. Because of that unfamiliarity, the sizing, access, design, installation, and maintenance provisions for tanks requires extra attention. Standards developers like CSA and the American Society of Agricultural and Biological Engineers have taken note and are hard at work on standards for these on site water tanks. The IgCC also contains numerous requirements that address these tanks.


• Collection Surfaces: Roofs are often ideal collection surfaces, but when it comes to rainwater, not all roofing materials are created equally. Proper selection is a careful balance between cost, intended use and locale. Information on acceptable materials can be found in the ARCSA Rainwater Catchment Design and Installation Standard and the IgCC.


Potential uses for rainwater span the gamut from non-potable to potable drinking water. In the end, local laws and codes will largely dictate uses in a given location. Plus, they establish any regulatory measures such as permitting, commissioning, water quality testing, labeling and signage. The IgCC provides model provisions but local requirements vary widely. Applications described in the IgCC include surface and subsurface irrigation, fire suppression, toilet and urinal flushing, ornamental fountains, and cooling towers.


In conclusion, rainwater harvesting represents an exciting and largely untapped source of water in a time of growing water needs. Like any technology, though, proper design and installation is critical to ensure safe operation and high performance. Documents like the ARCSA Rainwater Catchment Design and Installation Standards and the IgCC coupled with local requirements can form a solid foundation for these systems. For those interested in diving even deeper, ARCSA offers several levels of training culminating in ARCSA Certified Professional status. You can learn more about ARCSA or find their at www.arcsa.org and the IgCC at www.iccsafe.org/cs/igcc where you can download Public Version 2.0 of the IgCC for free.

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