Subsurface irrigation using graywater is preferable to spray irrigation, which “relies on a higher level of control and sophistication,” and would entail disinfecting the water for potential human contact, Muñoz says. The nitrogen in the wastewater is beneficial to the vegetation.
The Barrett development’s dense cluster of buildings was well suited for a laundry-to-landscape system because the graywater doesn’t have to travel far from the source to the reuse points. Traversing farther distances can be accomplished, but would require additional energy and infrastructure for pumps and plumbing.
Arizona’s climate also lends itself to year-round graywater systems. In colder climates, where landscaping requires less frequent irrigation and evapotranspiration occurs more slowly, or during periods of heavy rain, the saturated ground may be unable to absorb graywater, Muñoz says. “You want the ability to seasonally turn a valve and send it to the sewer. … A lot of systems have that option—whether automatic or passive—through an overflow storage tank [to release effluent] into the municipal grid system.”
Reuse and Reduce
Two projects of differing scales illustrate the potential of graywater recycling: Seattle’s Bertschi School Living Science Building by KMD Architects and New York City’s One Bryant Park by Cook + Fox Architects.
The 1,425-square-foot Bertschi School Living Science Building, a science wing for the school’s 235 students from pre-kindergarten through fifth grade, has a relatively simple graywater-reuse system designed by the Bellingham, Wash.–based engineering consulting company 2020 Engineering. Graywater collected from classroom sinks travels to an undercounter filtration tank. From there, the water is channeled to an indoor living wall of tropical plants, where it undergoes evapotranspiration (a return to the atmosphere through evaporation and transpiration from plant tissues). This closed-loop process eliminates the need for a storage tank. Students can experience water recycling, reuse, and conservation firsthand.
The building’s stormwater is also handled on site. A 2-inch-thick mat roof—comprising a thin moss mat, water-retaining fleece, and root barrier—absorbs and evaporates most of the rainfall during the summer, and between 20 and 50 percent of the rainfall during the winter. The balance drains into cisterns for use in irrigating an outdoor garden. The school also has the capability to treat rainwater to potable standards on site using carbon filtration and UV light, but the system is currently not used because the local health department did not approve the system.
The 2.1 million-square-foot, LEED Platinum–certified Bank of America Tower at One Bryant Park is, in many ways, a large-scale version of the Bertschi School. The building’s green roof collects excess rainwater used to irrigate plants indoors and to flush toilets. Gravity-fed collection tanks transport bathroom sink wastewater down to the tower’s basement for treatment and for reuse in the building’s cooling towers. Through a combination of low-flow plumbing fixtures and waterless urinals, in addition to the graywater recycling system, the project conserves about 7.7 million gallons of water per year.
Beyond regulatory approval, a shortage of time and poor planning are also obstacles to the widespread use of on-site water recycling systems, Muñoz says. “The problem comes when the client says, ‘This is what I want to do, but we don’t have any money to have a long permit battle and we need to have permits done in three months.’ ” Architects must anticipate an extended review period for wastewater recycling systems in their project schedules, he says, particularly in states and counties with cumbersome statutes.
The cost of on-site wastewater management can vary widely depending on the size and scale of the project, says Eric Lohan, general manager of Living Machine Systems, a Charlottesville, Va.–based company specializing in wastewater treatment and reuse systems through wetland ecology and, specifically, tidal pools. Adding to the complexity of estimating costs are variations in “the cost of water in a particular city,” Lohan says. “Water [utility] rates in general are growing at 9 percent a year. The ROI depends on how concentrated the water is, how much you’re treating, and where you’re located.”