Harvesting Rain: System Design for Strategic Rainwater Capture  

While developing Detroit's new Sugar Hill district renovations, Diane Van Buren, project planner and sustainable design coordinator at Zachary and Associates, has shown concern about the environment. Her focus has been on developing housing that will meet today's needs while still planning for the city's sustainable future. In order to meet her environmental targets, she has volunteered to be part of a new Detroit Water Sub-committee (WSC), a unit of city council member Ken Cockerel's Green Task Force. This committee has a framework of key issues that include developing community outreach, water conservation strategies and best management practices. The WSC is currently proposing downspout disconnection as an amendment to the City code in order to reduce the burden on the city's aging infrastructure that still has a combined stormwater and sewer system.

In the Sugar Hill District, approximately 950,000 gallons of rainwater will be collected from three rooftops and channeled through the small district for a variety of uses, including ponds and cisterns. The developers are seeking financing for the project through tax-increment financing allowable under the State of Michigan guidelines for stormwater control. This project will also highlight rainwater in sculptures to involve artists and the community in this new arts entertainment district. The challenge for these developers is to find the best design solutions for storing and distributing stormwater.

According to G. Edward Van Giesen III, ARCSA Registered Professional, MLA, policy coordinator for BRAE Rainwater Harvesting Systems, "a growing number of cities and states are rewriting their codes and making rainwater harvesting an essential part of their sustainability goals."

Design professionals can no longer create impervious surfaces independent of the variety of environmental effects that these surfaces cause. This represents a paradigm shift from thinking of water as something merely to get rid of to one that gives greater value to water and understands its intrinsic connection to the built environment."

Illustration courtesy of BRAE; Image courtesy of Lord, Aeck & Sargent, ©Jonathan Hillyer Photography Diagram illustrating rainwall harvesting system (top); The Grand Bay Coastal Resources Center in Moss Point, Mississippi obtained the USGBC LEED® GOLD rating in 2010 thanks in part to its rainwater harvesting system (bottom).

Rainwater is a national and global issue, whether there is too much rain or too little rain. Adapting strategic rainwater collection can conserve this natural resource. Defined in the Georgia Rainwater Harvesting Guidelines Manual, rainwater harvesting, in its essence is the collection, conveyance and storage of rainwater. Rainwater collected from roof surfaces and other above-ground structures is not "recycled water" nor is it "gray water," but an abundant source of fresh water, generally undervalued in the United States.¹

This article is about harvesting and integrating rainwater as a strategy to conserve water and save energy. There are many components to a successful rainwater system. These elements should be specified as an integrated system rather than a checklist of assembled pieces. Whether buildings are sited in dense cities, the suburbs or rural environments, rainwater harvesting can be a successful strategy for meeting many green building goals.

Grand Bay Coastal Resources Center: Highlighting Water Conservation

Archeological evidence reveals that for over 4,500 years, humans have lived in the rich biodiversity of the tidal estuary areas of the Grand Bay Natural Estuarine Research Reserve (NERR). The Grand Bay NERR, an isolated reserve on the Mississippi Gulf Coast, comprises some 18,000 acres of marshes, waters and coastal wetlands that are home to several rare plant and animal species as well as numerous commercial and recreational fish species. The land is owned and jointly managed by the U.S. Fish and Wildlife Service and the Mississippi Department of Marine Resources (DMR). Through its research and educational outreach efforts, the new facility supports the NERR's charter to promote stewardship of coastal resources using an integrated program of research, long-term monitoring, training and education. Image courtesy of Lord, Aeck & Sargent, ©Jonathan Hillyer Photography A view of the galvanized sheet metal storage tank used for rainwater harvesting at Grand Bay Coastal Resources Center. A new headquarters building, designed by the Atlanta offices of architects Lord, Aeck & Sargent in collaboration with Studio South Architects, serves as a center for scientists and students to test, observe and document the environment of this sensitive southeastern Mississippi nature preserve. The building was designed to reflect environmental stewardship of water resources. According to David Ruple, manager of the Grand Bay National Estuarine Research Reserve, "In an effort to reflect our environmental philosophy, I feel that it is not only important to do good conservation work but also to demonstrate how we can build and live more sustainably. I believe that the design and materials incorporated into our new facility will reflect that philosophy. We first had the idea of a green building in 2001 as we developed the master plan for the reserve. We were fortunate to receive the support and funding needed to build it as we envisioned. As we live in a very rainy part of the country, we feel it is important to demonstrate good water conservation practices, capturing and using that abundant rainfall on site." Environmental protection, water conservation and energy savings were important demonstration and educational components of this coastal headquarters. When the oil from the BP spill began to infiltrate the waters of this protected reserve, it became apparent that rainwater conservation was also a practical strategy. Rainwater from the roof is collected in two 6,500-gallon above ground cisterns and used for toilet flushing and for washing salt water from the Center's research boats. As part of the overall water strategy, the building also has dual-flush toilets, low-flow faucets, waterless urinals and native landscaping. In addition, a bio-filtration wastewater system was also installed as an alternative to a conventional septic field. By design, the Center is projected to use 76 percent less potable water and 53.5 percent less energy than comparable conventional buildings and 40 percent less purified water for toilets and equipment washing. Jim Nicolow, the director of sustainability for Lord, Aeck & Sargent commented, "One of the big challenges when planning for rainwater collection is that it doesn't really fit into the typical division of labor on a design team or a construction site. There is a potential gap between the civil and plumbing engineers and it can get muddy' as to who takes responsibility for the integration of the components. Involving a rainwater system manufacturer in the design process allows for more successful integration of a rainwater collection system." This headquarters building achieved LEED® GOLD in 2010, a confirmation of the NERR's commitment to the highest principles of environmentally sensitive design, construction and operation.

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Storage capacity designed to collect roof runoff and as part of an integrated design strategy Section courtesy of Lord, Aeck & Sargent

Water Conservation

There are many reasons to conserve water resources, such as recent droughts, floods and an aging urban infrastructure. Although water is an abundant resource in many parts of the temperate climate zones of the United States, numerous cities have aging infrastructures that include combined stormwater and sewer lines. With age and the increase of impervious surfaces, the systems of pipes, drains, catch basins and municipal treatment plants, are often overwhelmed when there is a heavy rain. Resultant flooding can cause back-ups into homes and businesses of both sewage and stormwater.

Chart courtesy of BRAE

Rainwater can be substituted for more than 65 percent of household water usage even if just for outdoor use and toilet flushing. If rainwater systems supplied just 15 percent of residential landscape irrigation in the U.S., one billion gallons of water would be saved each day.

The opposite problem occurs in the South and Western United States. Recent weather patterns resulting in historic droughts have reduced aquifers to dangerously low levels. Increased population in cities, the development of new suburbs in areas with a deficit of water resources and the increased demand of agriculture and mining on water resources, add incentives for even more water conservation measures and policies. By August 2000, 36 percent of the United States was in severe to extreme drought, leading to widespread wildfires and other drought-related damages. Instead of too much water, there is too little water to meet the demand for citizens and businesses in the South and Southwest.

Although rules and regulations on the state and municipal level are increasing, most states have an absence of any regulation regarding rainwater harvesting. This void in policy results in disincentives for architects, planners and contractors to incorporate rainwater harvesting in their projects.

One of the most common misconceptions is the definition of rainwater harvesting systems. There are still many regulators and design professionals that still refer to rainwater as gray water and apply gray water treatment standards to rainwater.

Global consumption of water has doubled every 20 years, more than twice the rate of human population growth. According to scientists, shrinking fresh water supplies present the most urgent and potentially catastrophic environmental problem today worldwide.² The 2006 worldwide average water consumption varies from large amounts of fresh water use by developed countries, to smaller amounts in less developed and less populated countries. The United States water consumption is approximately 570 gallons/per day per person, more than 6 times the amount used in China and substantially higher than most of the world, according to the United Nations Development report.³ In the twentieth century, water seemed to be an unlimited resource. Fresh water drives industrial processes and supports agriculture worldwide. According to the United Nations Environmental Program, buildings consume one-fifth of the world's available water.⁴ In the twenty-first century, designers are coping with limited water supplies and are learning how to design for smarter water use in buildings.

Rainwater harvesting can conserve water in most residential and commercial projects. Sixty-five percent of household water uses can be substituted for rainwater collected from roof surfaces. These uses include irrigation, toilet flushing, laundry and other nonpotable uses. As a response to dwindling water supplies and a respect for better stewardship of the environment, low impact development (LID) standards are becoming policy initiatives throughout the United States. LID practices encourage rainwater retention, close to the location where it falls to allow infiltration and cleansing. A rainwater harvesting system is designed to absorb and store water to release as needed. Through engineering, land planning, site design and the integration of building systems to resource management, the design professional can save water and enhance watershed hydrology.

Harvested rainwater is ideal for many exterior applications such as washing equipment or windows, irrigating plants and filling swimming pools. Although relatively clean, in all states, rainwater must be separated from the potable water lines to avoid cross contamination. In some states rainwater can be used to flush toilets, wash clothes and provide cooling tower makeup water. Rainwater harvesting reduces the volume of water flowing through aging municipal stormwater systems and decreases the nonpoint pollutant load that enters streams, rivers and lakes. In some states, rainwater can even be used for potable applications.

By storing rainwater, homeowners and businesses will have greater control of their supply of water during peak demand periods or during droughts. They will also see a decrease in their water bills and potentially, their sewage bills. Communities will have less water to pump, treat, redistribute and in many cases can delay upgrades to existing water supply infrastructure. Almost eighty percent of the cost of delivering water is energy according to studies by the Sandia National Laboratory. Conserving water will save energy, water, money and the environment.

Rainwater Systems: Calculating Resources

Rainwater collection should be thought of as a whole, not a collection of parts. Rainwater systems can be as simple as an above ground rain barrel attached to a downspout or as complex as a large underground storage cistern with connections and treatment options. The project budget, the end use for the rainwater, the demands of the project, the climate and the design aesthetics are some of the factors that will determine the type of rainwater system chosen by the project design professional or civil engineer. In addition, communities are developing new water regulations that may also affect the size and type of rainwater collection systems. Many western states are grappling with the issue of water rights. Unlike states with riparian water rights, many of the states that follow prior appropriation laws specifically prohibit the collection of rainwater. Recent legislation permitting limited capture in Colorado and mandating the use of rainwater in Tucson, Arizona are signs of new attitudes toward managing water resources.

Manufacturers of rainwater systems will assist design professionals as they set goals for rainwater collection and storage. How do you want to use rainwater? How much water can you collect by design? How much water do you need for your project? When sizing for rainwater capture, the design goal, whenever feasible, is to achieve water balance so that the volume of water collected equals or exceeds the volume of water used.

An optimal balanced rainwater system will lose the least amount of water to overflow during the wettest times of the year while maintaining some water in storage during the driest times of the year. The design must always take into account the budget and physical limitations of the site. Although it is possible to capture every drop of water from a collection surface, it may be either impractical or unnecessary to do so.

The National Weather Service Forecast Office⁵ publishes the annual amount of rain for communities. The American Rainwater Catchment Systems Association (ARCSA) also publishes detailed analysis on rainwater capture. Annual rainfall as well as its monthly distribution is important to consider when sizing a storage tank. Larger storage tanks are required in hot humid climates where rainfall is seasonal and in hot dry climates with long periods between storms. Smaller storage tanks may be adequate in a city like Portland, Oregon where there are frequent storms and steady showers. Regardless of the pitch, the shape or the complexity of the roof surface, the overall footprint of the building from eave-to-eave determines the catchment area. Approximately 0.62 gallons per square foot of collection surface per inch of rainfall is collected when it rains. The storage area for harvested water will approximately equal the catchment area (sq. ft.) X depth (in.) X 0.623. Proper maintenance, undersized or clogged gutters will also reduce rainfall collection.

Chris Kid's, Atlanta, GA

Chris Kid's is a nonprofit organization in Atlanta, Georgia that provides assisted housing for young adults. They installed a 19,000-gallon above-ground storage tank with a 6,000-gallon below ground sump to collect both roof water and surface water for irrigation.

Photo courtesy of BRAE Above-ground storage tank installation.

Storage Capacity

After determining the potential for rainfall capture, the design professional can begin to calculate storage capacity. As seen in the table from the Georgia Rain Water Harvesting Guidelines, the total storage in gallons will vary according to the amount of rain and size of the storage tank. The storage tank may need an initial deposit if installed during a dry season. Therefore, it is best that a cistern be installed as early as possible during the building process to take advantage of rain events. Demand and supply will vary month by month based on the amount of rainfall received into the system as well as the users of that system.

Architects can increase the catchment surface area with awnings or canopies as well as increasing the footprint of a building. Catchment surfaces can also include rooftop solar or hot water photovoltaic panels. Based on the amount of rain and the demand for water, rainwater systems are designed to meet performance targets as considering budget restraints.

Estimating Demand

Rainwater systems can provide water exclusively for outdoor use or for a variety of uses in buildings or for both. According to the American Water Works Association (AWWA) Research Foundation, North American households use approximately 146,000 gallons of water annually. Of this amount, 42 percent is used indoors and the remaining 58 percent is used outdoors. By far the largest percentage of indoor water use occurs in the bathroom for toilet flushing (18.5 gal/person/day) and showering (11.6 gal/person/day). Clothes washers were the second largest water users (15 gal/person/day).⁷

A study by the North Carolina Department of Environment and Natural Resources calculated that commercial, industrial and institutional uses accounted for as much as 40 percent of total municipal water use. Facilities were using as much as 20 percent of the potable water for cooling and heating. Other intensive water uses included irrigation and restrooms.⁸

Water conservation and efficiency are two parts of the same demand equation. Architects and engineers should combine their specifications of energy efficient plumbing and water saving equipment along with an efficient rainwater harvesting system. WaterSense is a new EPA partnership program with manufacturers that identifies products, programs and practices that conserve water resources. Many WaterSense products also provide rebate programs in many areas of the United States. Sizing demand for water using a rainwater harvesting system includes the incorporation of best practices for water conservation. Rainwater used inside a building is typically filtered and treated to a higher standard than rainwater used outdoors for irrigation.

The climate zone, type of plants and outdoor activities like equipment washing determine the demand for outdoor water use. To reduce the demand for irrigation, many design professionals are choosing plants that are native to the climate zone or designing xeriscapes that require very little water. Rainwater that is collected from pavement surfaces should be separated from rainwater collected from roofs if the resulting water is used indoors. In general, rainwater collected from roofs is lower in contaminants than that from surface water.

The demand for indoor water use includes using water for flushing toilets, as well as for cooling tower make-up water. In some states, rainwater can also be used for clothes washing and drinking water. Water expert Peter Coombes has studied both the benefits and analyzed the health risks for the use of rainwater. His studies have shown that the quality of rainwater meets most governmental water standards for clean water. Properly collected and stored rainwater is ideal for showering/bathing, laundry, toilet flushing and drinking. Although widespread use of rainwater has been hindered by uncertainty over quality and the perceptions of health risk, more research is demonstrating that rainwater can be used for many building uses.⁹

Graphic courtesy of BRAE Diagram of a residential above-ground rainwater system

System Components

There are six main design components in a rainwater harvesting system.

• Collection or catchment surface
• Gutters and downspouts
• Downspout filtration
• Storage - above and below ground
• Pumps and controls
• Treatment and disinfection

Collection Surfaces

Rainwater for the Garden

In 2009, water levels in Georgia were at record lows and residents were encouraged to conserve water. This homeowner in Watkinsville, Georgia installed a 1500-gallon above-ground polyethylene tank to water their garden, flush toilets and wash clothes. The system included an internal pump, first flush diverter, floating suction, related controls and the tank, which was hidden under the homeowner's backyard deck.

Photos courtesy of BRAE Rainwater storage is placed under the deck and the hose bib is carefully labeled as nonpotable water to be used for irrigation only.

Metal, clay, asphalt, wood, tar, slate, vinyl or rubber-the type and texture of a roof surface will affect the quality of the water runoff. A smooth surface will allow for more water collection and limit the possibility of evaporation or overflow from gutters. Powder-coated metal roofs have a smooth surface and resist corrosion, outperforming most other choices for a rainwater system. Tile, slate and clay roofs are porous and can lose as much as ten percent of potential rainwater due to absorption, insufficient flow or evaporation. Sealants can increase the flow on a porous surface and some coatings have a catalyst that neutralizes bacteria on a roofing surface. Green roofs do not make good surfaces for rainwater capture as they absorb much of the rainwater to provide plant moisture as well as contain particulates from the growing matter. When collecting water from green roofs the water is best used for outdoor irrigation purposes.

Many residential roofs have asphalt shingle roofs. As the roof ages asphalt grit is washed into downspouts. It is important to keep as much of this grit as possible out of the storage vessel. Most commercial roofing has a vinyl or rubberized surface with thermal or chemical welded seams. Design professionals should always take into account the end uses of the water before determining how or whether or not the composition of the roof will affect the quality of water collected. The end use for the water will determine the feasibility of using a particular roof system.

Gutters and Downspouts

Roof gutters and downspouts direct the flow of rainwater to the catchment area. Steep roofs, long distances between downspouts and inadequate maintenance can cause water overflow and loss of rainwater capture. Securely attached to downspouts, continuous or seamless half-round gutters are the most efficient conveyors of rainwater. Common downspout and gutter materials include PVC, vinyl, seamless aluminum and powder-coated steel. The critical component of this portion of the rainwater system includes the drop outlet. A gutter drop outlet routes water from the sloped, horizontal gutter to the vertical downspout. Roof hardware, brackets and straps, keep the gutters and downspout fastened tightly to the building. Complex roof forms may have roof valleys that direct more water to a gutter area often causing water overflow. If necessary, overflow roof dams will increase rainwater capture. Gutters and downspouts should not hold any water in the summer or the winter months and the roof installed as per code to reduce ice dams.

Filtration and First Flush

Filters, simple screens and first flush diverters are part of a complete rainwater system. Rooftop rainwater is filtered at the roof level and in the downspout to collect debris and sediment before water enters the storage tank. Leaf screens are attached along gutters above the downspout. They keep large debris from clogging the water channel. They are usually made of plastic or wire mesh and need regular seasonal maintenance.

A downspout filter shaped like a funnel with a stainless steel screen filters roof runoff. This filter is installed just above the highest level in a storage tank or along the pathway of the downspout at a level that is most likely to be maintained by the owner. Strainer baskets with fine to course mesh filters can be placed into the inlet of a tank to provide additional filtering. The type of screening and filter mechanisms depends on the climate, leaf or other litter loading as well as how the rainwater will be used. If the building is in a climate where there are infrequent heavy rains, accumulated roof dirt will require greater filtering. Typically, less filtering is necessary for rainwater used for irrigation than when the end source is for indoor applications.

Located downstream from filters, a first flush diverter can direct the first flow of rainwater that may have collected roof debris, built up chemicals, sediments and bacteria to a landscape area and away from the storage tank. The chamber in the PCV standpipe fills to prevent the initial water flow from entering the tank. Sealed by a floating ball, additional rainwater is diverted to the storage tank. Rainwater from the first flush is drained away from the storage tank and the system is reset for the next rainfall. A first flush diverter improves water quality, reduces maintenance and extends the life of pumps and fixtures that use rainwater. It is important to note that if a first flush diverter is not regularly cleaned and maintained they may be of little value and may even negatively impact the system.

There is no one size fits all solution to the filtering of rainwater before entering the cistern. Ultimately the cleaner the water coming into the tank the better the water quality will be on the way out. Rainwater systems consultants will evaluate rainwater quality including acidity caused by pollutants when choosing a filtering system.

Storage Above or Below Ground

Concrete, wood, metal, clay and plastic water storage vessels come in many shapes and sizes. The storage tank or cistern is one of the most critical components of the rainwater system and generally the most expensive part of the system. The storage tank needs to be placed as close to the catchment area as possible and the size determined by calculations based on the demand, frequency of rainfall, surface area, budget and aesthetics. Water flows downhill and the placement of the tank in relationship to the catchment areas and filters is important for maximizing rainwater collection.

Graphic courtesy of BRAE Diagram of a below-ground rainwater collection system

Rainwater storage tanks come in many sizes and configurations. They include the following:

• Rain barrels are the most widely chosen type of storage by homeowners. They can come in many sizes and typically a 55- to 75-gallon drum is used to water plant beds. For greater storage, barrels can be linked in series.
• Galvanized sheet metal tanks are often chosen for urban or suburban locations. Some designers like the rural look of these corrugated round tanks. They are available in sizes from 600 gallons to over 600,000 gallons and are lightweight and simple to build. The larger tanks might be used for schools or high-rise buildings. If zinc coated they are corrosion resistant and the interior can be fitted with a PVC liner or coated with approved paints.
• Wooden tanks are also a popular design choice for residential water storage. Reminiscent of railway water towers, they are available in sizes from 1600 gallons to 97,000 gallons. Wrapped with steel cables, these pine, cedar or cypress tanks are site built and lined with plastic or vinyl liners.
• Above-ground polyethylene tanks are available from 300 gallons to 10,000 gallons. These tanks must be opaque to be effective for water storage. When used below grade, they must have additional reinforcement to withstand soil pressures. Tank fittings and attachments are integral to the tanks.
• Fiberglass tanks are durable, easy to repair and can be placed both horizontally as well as vertically. They can be ordered in sizes up to 50,000 gallons. All fittings are integral to the tanks, avoiding the problems with retrofits.
• Polyethylene or polypropylene tanks are often chosen for in-ground installation. Polypropylene is more rigid with greater strength to weight characteristics and polyethylene is more flexible. Deeper installations require thicker walls and interior bracing. It is important to review and follow the manufacturer's guidelines for these tanks. Many underground polyethylene tanks for use in septic systems and sometimes considered for rainwater storage are unsuitable. They may need reinforcement, as sidewalls will collapse when they are empty.
• Concrete tanks can be poured in place or prefabricated. Structural engineers should determine reinforcing. A rainwater system must have a careful design for the entry and exit of water into the storage tank. Inevitably, some sediment will accumulate in the bottom of the tank even in the most well designed system. Usually a two 90-degree elbows are configured to turn up and direct water towards the surface channeling water via a calmed inlet to minimize sediment disturbance.

Water should not be extracted from the very bottom of the tank. This zone is known as the anaerobic layer. Water should also not be drawn from the very top of the tank due to the presence of floating debris. Water outlets are placed to extract water somewhere between the top and the bottom of the tank storage area.

Chart courtesy of BRAE

33,000-gallon underground aluminized-coated corrugated metal tank installed at the University of Georgia, Athens campus for site irrigation

Tanks must be opaque, as small amounts of sunlight along with the presence of organic materials will cause algae growth. They need to be tightly covered and sealed to prevent insects and contaminants to enter the tank. Lids should be tightly fitted and sealed to prevent unauthorized access especially children. All cisterns and storage tanks, either above or below ground must be accessible for cleaning and maintenance.

Local codes may influence whether a tank can be installed above or below ground and whether it will require screening. The height of the water table as well as soil quality will also influence the placement of a tank and designers should review the geology of the site during the planning phase. Consider the following when locating a rainwater storage tank:

• Manufacturer installation guidelines
• Prevention of overflow into a septic system drainfield
• Adjacency to supply and demand
• Maintenance
• Accessibility for installation and/or removal
• Placement on a level pad
• Placement in an area not prone to flooding or erosion

By treating a rainwater harvesting system as an integrated part of the overall site and building design, design professionals can develop site "watersheds." A designer may divert rainwater runoff from ground surfaces to landscape areas and separate this rainwater from filtered and stored rainwater catchment from roofs used indoors.

The design of the roof can also be seen as part of the design of the rainwater system. Roofs can be sloped to provide multiple zones or roof watersheds that are integral to both the design of the building as well as the rainwater system. The rainwater system can drive design decisions rather than follow design as an environmental add-on merely to gain points in a green rating system.

Chart courtesy of BRAE Multiple 3,000-gallon tanks along the roof's edge collect water for outdoor irrigation at Pine Crest School in Fort Lauderdale, Florida.

Pumps and Controls

Household water pressure can be obtained in a rainwater harvesting system by the use of pumps, pressure tanks and switches. Pumps draw and pressurize water from a storage tank to channel it into a piping network or additional storage tanks. On-demand pressure tanks are included as needed. Pumps need to be sized to deliver the flow and pressure required by a plumbing system, particularly for toilets. In both cases, backflow preventers are required. In all cases piping for drinking water should never be connected to the rainwater system used for equipment and mechanical systems in buildings to avoid contamination. A rainwater storage tank can be thought of as a well even if it is above ground. A properly sized pump will function as a domestic well pump supplying water on an as needed basis.

Water Quality and Treatment

Chart courtesy of BRAE

Children learn about ecology as they pass this rainwater harvesting system which is prominently placed at the entrance to Pine Crest School in Fort Lauderdale, Florida.

Rain is part of the hydrologic cycle of the earth. The sun heats water in oceans, water evaporates and becomes water vapor and plants add water to the atmosphere through evapotranspiration. As air currents move water vapor around the earth, the water particles collect, collide and fall back to the earth as rain and snow. Rainwater that falls on roof surfaces is relatively uncontaminated and studies have shown that most rainwater can be easily treated for indoor and outdoor uses.

For outdoor irrigation, some states require the rainwater to be treated to the same standards as graywater when applied to above ground irrigation systems. This is rapidly changing as codes are updated and modified. For indoor applications, some states require the water to be disinfected even for non-potable uses inside an occupied facility. That includes use for toilet flushing, as well as outdoor cooling tower make-up. This is primarily due to the potential of human contact with the rainwater.

Many states require treatments to control microbial growth and to prevent minerals from clogging plumbing fixtures. Rainwater systems will have a series of filters to reduce the presence of suspended material in the water. After filtering, rainwater can be disinfected by exposure to ultraviolet light, carbon charcoal filters, boiling or chemical treatments such as with chlorine or iodine. Ultraviolet disinfection sterilizes water and kills microorganisms that may be present in the water in enclosed, sealed pressurized units. Although sunlight has ultraviolet rays, it must be prevented from entering storage tanks because of potential algae growth and contamination.

The American Rainwater Catchment Systems Association (ARCSA) is a professional organization that is a source for detailed information on worldwide treatment options. ARCSA's mission is to promote sustainable rainwater harvesting practices to help solve potable, non-potable, stormwater and energy challenges throughout the world.¹⁰ ARCSA also provides resources, research, education and professional certifications and training.

Return on Investment and Celebrating Rainwater

A study from Australia funded by the United Nations Economic and Social Commission for Asia and The Pacific compared the safety of water from city water supplies with the decentralized capture of rainwater from roofs. Concerned about climate change, researchers reviewed opportunities for a "more resilient urban water supply." The study concluded: "urban water strategies should also consider the synergistic benefits of combined strategies (such as water supply from rainwater harvesting and from dams) which include improved reliability of urban water supplies and the potential to buffer the impacts of expected climate change."¹¹

The researchers proposed an eco-efficient delivery of water in the urban infrastructure and a systems approach that minimized costs and environmental impacts across multiple scales. This required a hierarchy of water management beginning at the local scale or source and finishing at the regional scale as a last resort. This approach is dependent on meeting multiple objectives for water security, economics, well-being and protection of the environment at a range of scales.¹² Experts continue to find challenges for water management, particularly in light of the 2010 flooding in Queensland, Australia that followed a severe drought in other parts of the country.

One of the most commonly asked questions by owners considering investing in a rainwater harvesting system is what is the return on the investment? Financial return is often based on the offset of the cost of municipal water. In smaller residential systems, the payback in dollars may not equal the investment over time but in larger commercial buildings, the payback can be substantial. In addition to economic benefits, owners are deciding to choose to conserve water to achieve green building certification, to have greater control of their water supply or just wanting to "do the right thing."

Another way to look at the ROI for rainwater capture is to incorporate the tax benefits for consumers. Stormwater management can mean the construction and repair of drainage systems and treatment plants and add to the tax burden of the entire community. Some cities provide tax incentives as well as a reduction in utility rates for the construction of rainwater systems. Individuals and businesses will find savings in their utility bills, have greater control of water availability and find a source of high quality irrigation water without tapping into community water systems. Georgia, Maryland, Texas, Virginia and Hawaii are states that provide rainwater manuals and design resources. Rainwater harvesting is a common sense method to preserve water. Design for rainwater harvesting protects water quality, prevents stormwater runoff, reduces groundwater withdrawal from underground aquifers and conserves valuable drinking water resources.

Architect Celeste Allen Novak AIA, LEED AP specializes in sustainable design and planning in Ann Arbor, Michigan.

Founded in 2003, Oakboro, NC-based BRAE is a leading provider of configurable rainharvesting systems and related technology for residential and commercial applications. Using collected water for flushing toilets, irrigating lawns and watering gardens can reduce water consumption by up to 65% in homes and buildings. BRAE is an active participant in the rainwater community and assists customers in adopting this technology for their applications. www.braewater.com