Irrigating With Non-Potable Water
Editor’s note: This article first appeared in the November/December 2011 edition of Water Efficiency.
Not so long ago, it seemed that there would always be plenty of fresh water to go around. Parents filled up and emptied inflatable swimming pools, children played in lawn sprinklers for hours, and cars were washed in driveways every Saturday without so much as a moment’s hesitation. Water seemed like one of the most abundant resources on earth.
In reality, however, only 1% of the world’s water is suitable for consumption. And to make matters worse, the world’s population in 2010 had grown so large that an estimated one-third of all people now live in a region experiencing water shortages. That translates to 1.1 billion people without reliable access to fresh drinking water in developing countries alone.
Why so many water shortages? Any region—even one that usually gets plenty of moisture—can experience unusually dry conditions that impact even the most robust water supply. Much of the southeastern United States typically averages over 50 inches of precipitation per year. Yet this area was hit by a particularly lengthy drought in 2007, causing counties and states to battle over fresh water reserves. Drought isn’t the only cause of water shortages, however. In 2005, the Census Bureau projected that approximately 88% of US population growth between 2000 and 2030 will occur in Sun Belt cities like Las Vegas, NV—a metropolitan area which grew from a population of 164,674 in 1980 to 478,434 in 2000, yet averages a mere 4 inches of rain each year.
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Regardless of its cause, the scarcity of potable water has become front-page news worldwide, and efficient water use is no longer just a nice idea—t’s an absolute must. Water prices in the US have risen by 30% over the past five years, a number that’s likely to increase in the years ahead. As potable water becomes more scarce and expensive, its use is now subject to scrutiny. In the US, it’s estimated that one-third of all domestic water use can still be attributed to landscape irrigation—a number that’s often higher in warmer climates. As a result, landscape-watering restrictions are often the first indication that an area is experiencing a water shortage. Still, landscapes and green spaces themselves have an intrinsic value that cannot be denied. According to Project EverGreen, an organization committed to informing the public about the positive effects of well-maintained green spaces, landscapes can increase property values, decrease air pollution, control soil erosion, and boost tourism. Clearly, landscapes are still worth creating and maintaining.
The Case for Non-Potable Water Use
It obviously makes sense to consider alternatives to fresh water for landscape irrigation. That’s where the use of non-potable water comes into play. Non-potable water includes water harvested from air-conditioning condensate, rainwater, stormwater runoff, and in some communities, treated commercial and residential wastewater.
The use of this type of water has experienced a surge in popularity, partly due to the United States Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED) Program. Sites seeking LEED Certification can receive anywhere from six to 10 certification points by using recycled water and implementing water efficient irrigation systems. LEED-certified properties save significant amounts of water and energy, and boasting this certification can help these properties appeal to the growing number of individuals and organizations concerned with environmental stewardship.
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Doug Bennett, member of the USGBC Water Efficiency Technical Advisory Group and water conservation manager for the Southern Nevada Water Authority (SNWA), says that the green building movement is increasing at a rapid pace, and nowhere is that more evident than in the water sector. “In earlier versions of the LEED program’s published standards, developers were often given the choice of using potable water through efficient products and designs, or substituting the water supply with an alternative source,” he explains. “Today, we’re moving ahead with the philosophy that all water needs to be used efficiently, regardless of its quality and source. It’s no longer an either/or proposition.”
While pursuing LEED certification is voluntary, some state and local agencies are mandating that new commercial properties and government facilities use non-potable water. The city of Tucson, AZ, for example, now requires that 50% of the water used by all new commercial building sites for landscape irrigation harvest must be non-potable. Many other communities are offering tax incentives and rebates to both residential and commercial buildings that use non-potable water. When you combine these incentives with the rising cost of municipal water and sewer services, it’s likely that using non-potable water for landscape irrigation will soon be the norm rather than the exception.
Getting Down and Dirty
When it comes to irrigation in the US, the term “non-potable water” actually covers a number of different types of water, the most common of which are brackish water, harvested water, and reclaimed or recycled water. Brackish water is a combination of fresh and sea water, obviously more commonly used in coastal regions. In most cases, brackish water must undergo reverse osmosis to remove excess salinity before it can be used for irrigation. Harvested water is collected through passive means–such as a rain barrel, green roof, or vegetative swale—or active means. Active water harvesting involves the use of mechanical systems to collect, filter, store, and recycle rainwater, stormwater, cooling system condensate, and “greywater”—water that has already been gently used for the purposes of hand-washing, showering, bathing, dishwashing, or laundry. While commercial buildings in many parts of the country are being encouraged to implement their own onsite water harvesting systems, reclaimed water remains the most popular type of non-potable water used for landscape irrigation. Reclaimed water is typically treated wastewater, the final product of a multi-stage treatment process. Instead of having to collect and monitor their own non-potable water supplies, irrigation sites in certain communities can now hook up to a separate supply of reclaimed water that’s constantly being collected and treated by their local water authorities.
What does the trend toward non-potable, reclaimed irrigation water mean for specifiers, landscape architects, and contractors? It’s likely that professionals who haven’t yet designed and implemented irrigation systems for use with non-potable water soon will. Because non-potable water has different chemical properties than fresh water, its effects on the site’s turf, trees, plants, and irrigation system components must be considered. Professionals will not only need to understand the complexities of non-potable water, but they’ll also need to learn how this process affects irrigation system components and design.
Research and Development
Reclaimed water often contains nitrogen and phosphorus that serve as a fertilizer for ornamental plants and grass. However, reclaimed water is also likely to contain other constituents such as salts, minerals, and sulfur byproducts like hydrogen sulfide and sulfuric acid. Because these constituents can build up within water supply lines, these lines must frequently be “shocked” with disinfectants like trihalomethane. While disinfectants may retard microbial growth, actual constituent levels present in reclaimed water can still vary widely depending upon when the supply was last treated. For the same reason, it’s also difficult for authorities to enforce maximum constituent levels. All of these factors not only make reclaimed water unfit for consumption, they can also have a potentially harsh effect on water transfer lines and irrigation system components. According to Greg Palumbo, senior product manager for Rain Bird Corporation in Tucson, irrigation system components have come a long way since the initial days of using reclaimed water for landscape irrigation.
“Initially, when reclaimed water consumption for landscape irrigation was growing and treatment plants and conveyance systems were increasing capacity to reliably deliver more water, the market demanded products that had features to indicate non-potable water usage such as purple parts, purple valve tags, and purple pipe,” says Palumbo. “At the time, updating irrigation products to provide only non-potable water use indication was enough. Our customers were quick to let us know, however, that indication was not enough. Today, we provide an array of products that offer increased protection from the higher concentrations of corrosive chemicals, sand, and debris found in many sources of non-potable water.”
To make products that withstand all sources of non-potable water, engineers at Rain Bird researched reclaimed water’s composition to determine what chemicals and compounds had the most damaging impact on the performance of products like valves, rotors, and sprays. They also studied the impact of topically applied chemicals such as pesticides, fertilizers and herbicides. Their findings showed that many of these chemicals, and the biological contaminants that feed on them, damage components and reduce product life expectancy. As a result, Rain Bird’s engineers developed tests to accelerate degradation and simulate real-world conditions, later comparing these results with recovered field samples to correlate the acceleration level with actual exposure duration.
The results of Rain Bird’s research were particularly useful during material selection for the company’s new RD 1800 Spray, a product designed specifically for use in non-potable applications. Palumbo says this new spray can withstand challenging non-potable system installations without excessive embrittlement and degradation. However, Palumbo’s team knew that while it’s certainly important to make non-potable irrigation components more durable, it’s also important that they be as efficient as possible, making the most of every drop of water. “To enhance the RD1800 Spray’s reliability, especially in applications with sand and debris, we used modern design software to precisely engineer the wiper seal and stem interaction,” says Palumbo.
The Future of Reclaimed Water
The use of reclaimed water for landscape irrigation is not simply a trend that will quickly come and go. It’s likely that future water shortages both in the United States and internationally will continue, making it necessary for all of us to reduce the amount of potable water we use for irrigation. It’s also likely that green building initiatives like the LEED program and future legislation will continue to encourage architects, specifiers, and builders to include non-potable irrigation systems in their site plans.
“I strongly encourage landscape and irrigation professionals to familiarize themselves with the concepts being promoted and add their voices to the process,” says SNWA’s Bennett. “Professionals should not consider LEED as a boutique product. More and more codes and standards are being developed that use similar approaches. What was LEED today may be code tomorrow.”
Beyond the LEED program, recent legislation such as California’s AB1881 and Model Water Efficient Landscape Ordinance and EPA’s WaterSense initiative have been driving demand for better, more durable landscape irrigation products specifically for use with non-potable water. Palumbo says that this presents manufacturers like Rain Bird with an incredible platform to promote premium, water-saving products to increasingly savvy customers.
“A significant challenge for the landscape and irrigation industry lies in the interpretation of well-meaning legislation and ordinances, as there is often the perception that the only way to meet requirements is to eliminate turf and landscapes,” adds Palumbo. “Projects with landscaped areas offer tremendous environmental benefits. Educating our customers is vital to protect and maximize the amount of landscaped areas while meeting legislated requirements.”
The drip/micro irrigation company DIG Corporation’s product lines promote water savings and sustainability, says Benjamin Raines, marketing manager. Of particular note:
“Customers are looking to save water and therefore money, and are beginning to understand how water is not a finite resource and needs to be used wisely,” says Raines. “In the same thought, landscape professionals—from architects through contractors—want to provide more water saving options in their designs and working landscapes.
“The LEED rating system, created by the US Green Building Council, is also a promoter of water savings and sustainable design, resulting in an increased demand for these types of products,” he continues.
Raines points out that no matter how automated systems become, they still must checked frequently to ensure they are operating as designed.
“The new products available today make it much easier to accurately keep landscapes healthy and lush using less water, but they will never substitute an onsite visual inspection,” he says.
Municipalities are increasingly looking for new ways to make their irrigation systems more efficient, from new installations to converting old systems, Raines notes.
“Smart controllers, weather stations, and rain sensors are becoming much more prevalent with each passing year. With water restrictions increasing, as well as the cost, it is imperative that municipalities invest in new water-saving technologies,” he adds.
Keeping the public informed on water saving methods and that there is always a need to conserve is key, says Raines.
“Most landscape professionals are aware of water shortages, but the public needs to be reminded that we must use smart water practices in an effort to conserve,” he adds.
The Irvine Ranch Water District: Pioneering Reclaimed Water Use
In 1963, the Board of Directors of Southern California’s Irvine Ranch Water District (IRWD) developed a plan to integrate water recycling into the local community’s overall design. By 1967, the IRWD’s Michelson Water Reclamation Plant was providing two million gallons of reclaimed water per day for agricultural irrigation. By 2008, the Michelson plant’s capacity had risen to 18 million gallons of reclaimed water per day.
Today, the IRWD covers a 179-squaremile service area with more than 4,000 reclaimed water connections. According to Nick Mrvos, landscape water conservation specialist for the IRWD, his agency now provides reclaimed water not just for agriculture, but also for industrial purposes, toilet flushing in commercial buildings and landscape irrigation. “Today, we deliver more than 23.5 million gallons of recycled water per day to over 4,000 customers,” says Mrvos. “Reclaimed water makes up more than 20% of the Irvine Ranch Water District’s total water supply.”
Even though higher energy costs and increases in the costs of water treatment have caused the price of reclaimed water to rise by 2% to 3% over the past eight years, the IRWD is still able to provide its treated water at a very attractive rate. “We charge approximately 10% less for our reclaimed water than our potable water,” says Mrvos. “But that’s partially due to our unique allocation and tiered rate system. Our base rates are among the lowest in Orange County.”