Harvesting Rainwater New Codes & Design Standards
The topic of water shortages is nothing new as cities around the globe struggle with drought, water quality, supply constraints and failing infrastructure. However, the idea of new plumbing codes and design standards working together to assist plumbing engineers in adding harvested rainwater systems to their design arsenal has been uncharted territory – until now. With the publication of the 2010 IAPMO Green Plumbing and Mechanical Code Supplement (GPMCS), 2012 IAPMO Uniform Plumbing Code (UPC) and the Rainwater Catchment Plumbing Engineering Design Standard by the American Rainwater Catchment Systems Association (ARCSA) and American Society of Plumbing Engineers (ASPE), the plumbing industry now has authoritative tools at its disposal to standardize safe and reliable use of rainwater for potable and non-potable applications.
Rainwater harvesting provisions were introduced in the GPMCS and the UPC by the IAPMO Green Technical Committee (GTC) as part of a broader effort to reduce energy and water consumption of plumbing and mechanical systems while ensuring these systems are safe and reliable. GTC is comprised of the broadest group of expert stakeholders ever assembled to develop sustainable plumbing and mechanical requirements.
Although rainwater harvesting is an ancient practice, it has never been directly addressed by national plumbing codes. It appears that rainwater usage began to disappear in many parts of the world with the rise of urbanization, centralized supply systems and the need to meet the escalating demand for safe and reliable potable water supply. When national codes began to emerge in the 1900s, rainwater harvesting was not a common practice in metropolitan areas, and, as a result, rainwater harvesting was never specifically addressed. The lack of direct coverage in the codes has been one of the primary hindrances to the use of harvested rainwater.
The timing of the completion of the 2010 GPMCS, 2012 UPC and the ARCSA/ASPE design standard couldn’t have been better as the escalating stress on available water supplies has spurred a flurry of legislative and regulatory efforts across the United States aimed at permitting use of rainwater as a means of off-setting some of the pressures on more conventional potable water sources.
One of the more notable and high-profile examples of these activities is California Assembly Bill 275, The Rainwater Catchment Act of 2011, which seeks to permit the capture and use of rainwater for non-drinking purposes in California. (At the time of the writing of this article, the California Legislature has passed AB 275, and the bill is awaiting the governor’s signature.) AB 275 requires that the installation of systems for indoor non-potable use of rainwater must comply with the requirements set forth in the IAPMO Green Supplement.
Additionally, definitions and other bill requirements came directly from the ARCSA/ASPE Rainwater Catchment Plumbing Engineering Design Standard. Availability of these documents ensures that strong and consistent codes and design practices are in place and gives legislators the confidence they need to pass bills like AB 275.
What Codes & Standards Cover
Application. To start, GPMCS and UPC contain identical provisions establishing that rainwater collected from roofs or other above-ground manmade surfaces is permitted to be used for non-potable applications, including toilet and urinal flushing, trap priming, irrigation, industrial processes, water features, cooling towers and other applications approved by the authority having jurisdiction. The section addressing rainwater applications is intentionally broad to also permit its use in car washes and automatic fire sprinkler systems.
In a separate appendix, GPMCS and UPC provide comprehensive requirements for use of rainwater for potable water applications in homes and businesses. In instances where rainwater contacts parking lots, driveways, pedestrian surfaces and other ground surfaces, GPMCS and UPC require more rigorous filtration and treatment methods before it can be used for plumbing and irrigation applications. Rainwater contacting these surfaces is handled differently because run-off may contain additional contaminants and health risks (e.g., oils, road salts, debris, hydrocarbons and pathogens) that require unique or enhanced treatment strategies. This approach was taken to mirror the scope and intent of the ARCSA/ASPE design standard, which does not apply to collection of rainwater from vehicular and similar surfaces.
Maintenance, Testing & Inspection. GPMCS and UPC require rainwater harvesting systems to be inspected, tested and maintained regularly and to establish a minimum frequency for these activities to occur. These documents assign compliance responsibility to the property owner or a designated appointee. Finally, a maintenance log that includes a record of inspections, testing and maintenance is required to be kept up-to-date and on-site at all times for inspection.
Backflow Prevention and Cross-Connection Control. Because of heightened cross-connection and public health and safety concerns, requirements address protection of potable water supply against cross-connection. Rainwater systems are not permitted to have direct connection to any potable water supply or alternate water source system. Potable or reclaimed (recycled) water is permitted to be used as makeup water for a rainwater catchment system, provided the potable or reclaimed (recycled) water supply connection is protected by an air gap or a reduced-pressure principle backflow preventer. Where any portion of a rainwater system is installed within a building, a cross-connection test is required to ensure an inadvertent connection between potable and non-potable rainwater systems hasn’t occurred.
As a final level of protection, rainwater piping systems are required to be identified with the wording “Caution: Non-potable Rainwater, Do Not Drink” and have a purple-colored background.
System Design. GPMCS and UPC require the pressurized portion of the rainwater system delivering water to the plumbing distribution system to be installed in accordance with the water pipe sizing provisions of the plumbing code. They also require gutters, roof drains and rainwater conveyance pipe to be sized as storm drains in accordance with the plumbing code.
GPMCS and UPC reference the ARCSA/ASPE design standard for guidance on estimating the potential for harvesting rainwater at a particular site (determining the maximum amount of rain that can be collected), estimating demand and properly sizing storage tanks. Comprehensive and harmonized provisions addressing above- and below-grade storage tank locations, supports, materials, construction, drainage and overflow, access openings and markings are provided in the GPMCS, UPC and ARCSA/ASPE design standard. GPMCS and UPC also contain provisions addressing algae control, vermin protection, rainwater discharge into sewer systems, debris filtering and removal, first-flush devices and roof washers.
The most important goal of the GPMCS, UPC and ARCSA/ASPE design standard is to ensure the output water meets a safe level of quality for the intended application. Numerous treatment devices and strategies are available to system designers that can be used to accomplish this. Although GPMCS and UPC require adherence to minimum water quality standards for non-potable application, they provide flexibility in the use of treatment technologies, such as flocculation/sedimentation, filtration, chlorination, ozonation, ion exchange and UV disinfection methods. Again, GPMCS and UPC reference the ARCSA/ASPE design standard for additional guidance on various treatment technologies and associated design strategies. For potable applications, the GPMCS, UPC and ARCSA/ASPE design standard have very specific requirements and installation details for filtration and system disinfection.
In closing, with code obstacles eliminated, it appears that rainwater collection and use are poised to become mainstream as jurisdictions around the world turn to rainwater reuse to address intensifying water crises. The IAPMO Green Plumbing and Mechanical Code Supplement, Uniform Plumbing Code and ARCSA/ASPE Rainwater Catchment Plumbing Engineering Design Standard combine to provide the necessary tools for inspectors, installers and system designers to safely and confidently embrace and utilize rainwater.
Note: ASPE and ARCSA are well represented on GTC and played a critical role in development of the first model code provisions for rainwater harvesting. Jeffrey L. Ingertson, CPD, FASPE and ASPE vice president of membership, serves as ASPE’s official representative while Bob Boulware, immediate past president of ARCSA (and ASPE member), represents ARCSA. Larry N. Oliver, CPD, FASPE and former ASPE president, and April K. Trafton, president of Donald Dickerson and Associates, round out the slate of plumbing engineering members of GTC. Additionally, more than 20 sustainable plumbing engineering experts serve among the more than 125 members of the 12 task groups that operate under GTC.