Vol 3. 2012 – Building Green with Rainwater Harvesting

With escalating demand and strain on municipal water and sanitary systems, along with evolving green building requirements in the design community, it’s important to examine all aspects of a project, to determine the proper solution and fully realize the potential of a RWH system. This installment of Greenovation+ provides a brief overview of the benefits of implementing a commercial rainwater harvesting system, and the considerations that should be made by designers and building owners, before making the initial investment.

Rainwater Harvesting Practices as a Solution

While green plumbing equipment can help reduce our overall “water footprint,” and remains a viable solution to address conservation concerns, Rainwater Harvesting (RWH) is arguably one of the most promising green alternatives. The long-standing practice of collecting rainwater for future use has been adopted in many areas of world for over 4,000 years.[i]Whether to combat rising water prices, or ease water shortages, a RWH system can offer a diverse range of benefits for a building, and its local environment, by alleviating demand on the sanitary system, as well as reducing the total potable water supply costs.

Although RWH and grey water practices have been demonstrated to help address our water concerns, some designers and building owners are still reluctant to apply this concept into their building design, due to the lack of education on RWH systems, and the cost of installation, especially for existing infrastructure. Although these systems have been gaining traction in recent years, particularly in areas experiencing critical water shortages, such as arid states like California, RWH and grey water reuse methods are not yet widely implemented, and unfortunately, their use is often obstructed by state or provincial building codes.[ii]

With evolving LEED standards, and the general shift to green construction, areas of Europe, parts of Asia and the Caribbean continue to demonstrate the benefits, of water reclamation practices.  To achieve LEED certification, and secure long term sustainability, it is becoming essential to fully understand the benefits and the proper application of RWH systems.

“Reuse is key to the State’s water future. Currently, Florida is leading the nation — reusing 660 million gallons of reclaimed water each day to conserve freshwater supplies and replenish our rivers, streams, lakes and the aquifers,” said former Secretary Michael W. Sole. “In 2006, Florida’s Water Reuse Program was the first recipient of the EPA Water Efficiency Leader Award. Even as a national leader, Florida is only reaching a fraction of potential reuse opportunities. As our state continues to grow, DEP will strive to promote efficient water management to help conserve the State’s natural resources.”[iii]

A Snapshot of How a RWH System Works 

The concept of RWH is simple. Generally, water or rainwater that would have otherwise gone down the sanitary system, or into the ground, is collected in a catchment area (typically a roof) and directed through rainwater leeders to various forms of filtration. This removes sediment and debris while oxygenating the rainwater. The Rainwater then travels into a storage tank through a calming inlet which prevents the agitation of bio-film which has settled at the bottom of the storage tank.

Additional levels of sediment filtration and ultra-violet light (to eliminate bacteria) results in high-quality reclaimed water, which can then be used for water for livestock, irrigation, flushing toilets, vehicle wash and laundry, and also to replenish ground water levels. By implementing RWH systems into your next green building design, you will not only help protect our world’s water, but it can help you achieve potential LEED credits under various categories, including the “Water Efficiency”, “Sustainable Sites”, and “Innovation of Design” categories.

ATS' Rainwater Harvesting schematic
Above: ATS Rainwater Harvesting System Schematics. For full details, log-on to

Considerations of Implementing a RWH System

When considering a RWH system, it is important to know the nuances of how each system operates. Traditionally, RWH systems did not include pre-filtration devices, and collected water from the roof directly into the storage tank. This method carried the dirt and debris accumulated along the water’s path into the storage vessel, and necessitated regular clearing of the tank, greatly increasing the operational costs, and making it an unattractive investment. However, with recent advancements, most systems now include pre-filtration units, which eliminates the need to have a person enter the hazardous environment of the tank to perform a cleaning, thus reducing the maintenance costs.

Other questions surround the piping arrangement for the domestic make-up water. By design, some of the first RWH systems put the domestic make up water directly into the tank. This caused two main concerns: when the collected rainwater reached a low point where it is no longer being drawn from to serve the building, a float switch would activate the domestic water, filling the tank back to an adequate water level to restore supply to the building. However, if there was rainfall the next day, the rainwater might not be collected, as the water from the tank may overflow into the catch basin, reducing the very water efficiency that a RWH system is designed for. Additionally, chlorinated domestic water can adversely affect the ecosystem within the tank. With pre-filtration units installed, “good” bacteria will make it through the filter and into the tank. The bacteria will then settle on the bottom of the tank creating a bio-film. This organic bio-film will draw oxygen from the water, creating an anaerobic zone at the bottom of the tank. At the same time, a highly oxygenated aerobic zone is created in the middle of the tank, which is where the pump will draw water to supply the building system. Drawing from this aerobic zone within the tank provides healthier water for use. The chlorine in the domestic water would remove any of these natural benefits.

For existing buildings, it is also essential to consider the costs of installing an above or below grade storage tank, as the space available for an appropriately sized storage tank may ultimately determine the potential success of a RWH system and its return on investment. Educated building owners will often find that a willingness to invest in a higher initial cost of a properly sized tank, may yield greater long term financial and environmental benefits. Conversely, the allowable space in existing properties will have a significant impact on the size of tank selected. Properly sizing a storage tank is one of the biggest challenges in the designing a RWH system, and commands a thorough understanding of the building’s supply and daily demands, along with the necessary filtration.

Final Thoughts

With growing concerns over water shortages, in addition to tightening LEED requirements, it has become increasingly difficult to become LEED certified without the implementation of a RWH system. While the initial investment of a RWH system was cost prohibitive years ago, with increased knowledge and experience, manufacturers are becoming more competitive in price, increasing the attractiveness of these systems to building owners and designers today. To truly benefit from a RWH system, it must be accurately sized, strategically customized, and stringently audited, to maximize its practicality and ROI.

For a free information package/ product selection guide or assistance on specifying RWH products for your next project, please feel free to contact ATS.

i. Rainwater Harvesting. (n.d.). Retrieved June 2012, from Capital Regional District:
ii. Rainwater Harvesting and Grey Water Reuse. (n.d.). Retrieved June 2012, from CMHC Canada Mortgage and Housing Corporation:
iii. Water Reuse Program – FDEP. (n.d.). Retrieved June 2012, from Florida department of environmental protection:

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