or optimizing consumptive systems dropped the WUI to 15 gal/sf/ year, a nearly 50 percent reduction over the existing campus. Further reduction also would be achieved through reuse systems, with the captured and treated water used for landscape irrigation and the flushing of plumbing fixtures. All told, through best practices and more aggressive leadership measures, it was determined that the WUI could drop as low as 9 gal/sf/year. Further reduction, although possible, was determined not to be cost-effective and also counter to Denver Water's intent to use highly regulated, utility- provided potable water for all potable water uses. The final selected target would achieve nearly a 70 percent WUI reduction over the existing campus and a more than 75 percent reduction from the average building. The owner and the design team set these early-stage goals to ensure that all future decisions would facilitate a successful implementation. To address water use reduction, all plumbing fixtures were low flow using water; no waterless urinals or composting toilets were implemented due to the nuisance issues sometimes encountered with these devices. Specifically, the flow rates for the common plumbing fixtures were 1.1 gallons/flush (gpf) for water closets, 0.125 gpf for urinals, and 0.1 gallons per cycle for lavatories. Extra care and attention were paid to the selection of the commercial kitchen equipment to ensure that it also used low-flow components. Lastly, extensive use of native and adaptive landscape planting allowed for significantly reduced irrigation demands. For water reuse, the team first had to make sure that such reuse was allowed by local laws and a need for reclaimed water existed. Fortunately, local codes did allow for reclaimed water, and it would be used for typical nonpotable greywater uses, including flushing fixtures (urinals and water closets) and irrigation.
Water reclamation systems
Three types of water reclamation systems are typically considered on any project: greywater (capturing water from lavatories, showers/tubs and clothes washers), blackwater (capturing water from nearly any plumbing fixture, including those noted under greywater), and rainwater (capturing rainwater falling on the project site, primarily into the roof drains). Of these three, greywater and rainwater tend to be the most common across the United States due to their more simplistic treatment requirements and reduced hazards. For Denver Water, the team chose a plant-based blackwater system and a rainwater system. To provide a broader understanding of all the options considered, explanations of all systems follow. Greywater systems . Chapter 13, Nonpotable Water Systems, was added into the 2015 version of the International Plumbing Code (IPC) to govern nonpotable water systems such as greywater. This IPC chapter does an excellent job of walking through the requirements of the system, including, but not limited to, allowable and prohibited sources, allowable and prohibited uses, disinfection, filtration, makeup water, signage requirements, testing, operation and maintenance. A greywater system was not used for Denver Water as sources were limited, which is common for office buildings. Greywater-only systems can be more beneficial for hotels, apartments and other facilities with multiple showers/tubs and clothes washers. Blackwater systems . In addition to the sources identified for greywater, blackwater systems typically add in water closets, urinals, dishwashers, kitchen sinks and other more contaminated wastewater sources. Blackwater systems take reclamation to another level since it contains
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The Plumbing Engineer's Role
The plumbing engineer is only fulfilling one of many roles required to implement the design of water reuse systems; civil engineers, specialty reuse consultants, legal representatives, architects, contractors and many others all have a part to play. While there may be plumbing engineers with the experience and expertise necessary to implement an on-site wastewater treatment system, the typical plumbing engineer does not. It is recommended for the design team to bring in a specialty consultant and the contractor team to deliver the specific requirements required for the on-site wastewater treatment system. For rainwater, it is essential to understand specific water rights. In some states, rainwater capture is a more accepted practice with limited barriers to implementation. In other states, such as Colorado, implementing rainwater capture on a large scale requires detailed legal analysis and application of proper water rights.
Figure 2. Water master planning can outline a path to achievable water reduction goals. Photo credit: IMEG Corp. and Stantec
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