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space uses about 83 percent less tap water titan comparable Tucson landscapes. What's remarkable is that such savings weren't achieved with expensive high-tech equipment, In fact, the garden started life with a handicap: a landscape budget that was cur, just before construction documents were done, to exactly zero. Thau's right: Nada, ni un centavo, as it might be phrased here.

How is it possible to save more than three-quarters of the normal water budget while spending $0?

Water trickles from a steel channel, above, and as seen from the third floor, left, is reminiscent of traditional "canales" that drain roofs of this region's adobe buildings. A square overflow basin offers seating during the dry season. The channel supplies a pond and native plants, below.

The answer has two parts. The first is about using "found" water—and other materials—a strategy that the garden's designer, Christy Ten Eyck, FASLA, calls "living off the waste of the building."

That concept, in turn, brought together the Arizona landscape industry to make the cala garden happen, money or no money.

"You can't pick up a magazine today without reading alx>ut water harvesting," says Ten Eyck, whose firm has offices in Phoenix and Austin, Texas. It's surprising, chough, that collected rainwater isn'c che biggesc source of water in her design. The Underwood Garden gees only 30 percent of its water from the cala building's roof— a substantial amount, but not enough to nourish the plants there. Graywater, an increasingly popular source of irrigation water, contributes even less to this project, only 2 percent. Stoltz explains: "We have many young architecture studencs in che building, putting ink and concrece down the drain, a total mess." Graywater at cala

"Buildings," says Christy Ten Evck. I ASI A, "are the new aquifers. There are till these hidden sources of water that we never think about. "

comes only from drinking fountains, which remain mostly unpolluted.

So where does the rest come from?

Two sources, often overlooked in current discussions of sustainable water supplies, provide almost exactly half of the Underwood Garden's water budget. Air conditioners produce 95,000 gallons of condensate, essentially distilled water, each year. Back flushing of drmking-water filters contributes 45,000 gallons annually, laden with minerals that help balance the mineral-free distilled HVAC condensate.

That's 140,000 gallons of free water per year that, instead of flowing down storm sewers to disrupt some anonymous stream somewhere, fill a three-story tank built into the building and then infiltrate once-sterile soil, irrigating an urban educational landscape.

The Underwood Garden is a one-acre representation of five vegetation zones of the Sonoran Desert. Harvested water from the roof chutes dramatically into a pool sur rounded by desert riparian plantings. Then there are areas of wetland, canyon, Upper Sonoran, and mesquite basque plantings (bosque is the Spanish for woodland and is used throughout the Southwest to mean river-bottom habitat—the only place that shade trees grow in arid regions).

A 50-foot-tall, 200-foot-wide trellis covered with the southern Sonoran native

Calhteum macmptermn (Gallinita, or yellow orchid vine, also called Mascagtiia macrop-tera) shades what otherwise would be a glass-box facade—"not the most energy-efficient building," says Stoltz laconically. Wire mesh stays coot enough for the plants toclimb, unlike the tubular steel supports, which because of their greater mass heat up to scorching temperatures.

A central retention basin does double duty as an outdoor educational space. A seating area under thornless mesquites, popular with students and faculty, opens to the building's main entrance. Storm overflow runs through a series of microbasins, which slow the concentration of water and decrease the potential for flooding. Any surplus flow runs westward in a delilierately

The Tucson Water Picture

Like many desert cm es, Tucson has a dramatic water footprint. Impervious surfaces and imported plantings, plus human consumption of water, have all had their impact on the wafer cycle. Evaporation {from wet surfaces and water bodies) and transpiration (from plants) have increased measurably in parallel with development, as of course have storm water runoff and erosion problems.

The cala project is a good reminder that runoff, évapotranspiration, water quality, and water supply are not separate issues. The current demand for water in Tucson, according to the local public utility, peaks at 155 million gallons a day in high summer. The average single-family home uses roughly 100 gallons of water daily, of which 30 to 50 percent is used on landscapes. (An Arizona State University research and demonstration project called Casa de Ago a has succeeded in cutting residential use to 53 gallons a day.)

Because évapotranspiration exceeds precipitation, Tucson relies on groundwater, like virtually every desert metropolis. Stoltz refers to this as "drinking very high-quality prehistoric water." Tucson's wells can only supply 145 million gallons per day (about 94 percent of peak demand); reservoirs hold an extra day-and-a-half supply pumped from the ground during the cool season, plus stored surface runoff.

Tucson has a voluntary system that assigns odd/even days for landscape irrigation, covering residential and commercial landscapes- In a drought, water emergency legislation can make this system mandatory. The utility's web site (www.ci.tacson.az. us/tvater/irrig sched.htmj lists water conservation measures including rainwater harvesting but does not mention condensate orgraywater.

Today's sustainable design relies on reducing waste and on creatively reusing resources squandered by conventional systems. (For an example of creative repurposing of groundwater, see 'The Same River Twice," Landscape Architecture, September.) What happens tomorrow, when some of these conventional systems become less wasteful or are abandoned, is an important question in long-term water sustainability.

Pinnacle Rubber Mulch.

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As a decorative landscaping material, Pinnacie Rubber Mulch has the classic style of traditional wood muich with none of the weaknesses.

• Resistant to wind, water, sunlight

■ Reduces bug and rodent infestation

• Does not decompose/ compress

Apply once and eco-friend!y Pinnacle Rubber Mulch does the rest, providing years of plush and durable ground cover.

As playground safety surfacing, a 6-inch layer of Pinnacle Rubber Mulch will cushion a child's fall from as high as 12 feet.

• Will not cause splinters ■ Wheelchair accessible

• Long lasting and low maintenance

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rough channel past an adjacent building into larger drainage ways.

The channel, microbasins, and other parts of the garden are lined with Urban i te—that is, recycled concrete. Todd Briggs, project manager for Ten Eyck Landscape Architects, notes the parallel between this and found water: "We realized there was building material we could recycle, instead of paying some company that mines river rock and blows up stone." The jackltammered paving was initially placed by hand and looked chaotic (causing skepticism among the faculty) until finer decomposed granite was broadcast and allowed to settle into the voids. That and a little help from flowing storm water created a process-based naturalistic look that finally won over the design faculty and students.

The garden also attracts wild creatures. Hawks have been sighted hunting lizards and other prey. Stoltz, who monitors the place daily (and collects cigarette butts and

Virtual Water?

How CAN WATHR, the very stuff of life, be virtual? The new—and imperfect— concept of "virtual water" will interest anyone concerned with sustainable landscapes.

The production of most products requires water, whether for irrigating crops or rinsing computer chips. When a product is exported or sold, thart water may noi literally be in the package, but it is part of the product, much like embodied energy.

Only 6 percent of water goes to drinking, washing, and other household uses, while virtual water makes up the other 94 percent.

Economists and conservationists are starting to calculate the "waiter footprint" or virtual water content of products as an aid to understanding their impact on the earth's most precious resource. Some examples from "What's Your Water Footprint" in Mother Jones's July/August 2009 issue: I Cotton T-shirt: 719 gallons

Ream of white paper: 1,321 gallons I Pound of beef: 1,857 gallons

goldfish that people dump in the pond, which is a "safe harbor" for threatened fish species, under an Arizona Fish and Wildlife permit), says there is an incredible diversity of insect life, but no mosquitoes.

So why was there no budget? The CA1A building, like many on the University of Arizona campus, was built under a "Construction Manager at Risk" contract—a

Midsize car: 39,090 gallons Four-ounce coffee (how many ounces are in that venti?): 37 gallons Pint of beer: 20 gallons Microchip: 8 gallons

Landscape irrigation is usually included in household use, the 6 percent mentioned above, but there aren't yet any specifics about the water footprint of construction materials or processes or horticultural products. The landscape disciplines are, at the moment, behind the curve oil a useful new concept.

The Underwood Garden raises some interesting questions about virtual water. How do we account for condensate that is pulled out of thin air, recycled to irrigate plants, and then infiltrated? Embodied energy methods may offer a parallel: In analyzing materials, recycling creates an embodied energy credit, while disposal is a debit. Because water links so many things, accounting reliably for its landscape "footprint" will take ingenuity.

For further information, visit www. water footprint.org.

The outdoor classroom attracts both migratory species (students and faculty, above! and natives (roadrunner, below). Naturalistic and constructed geometries and natural and reconstructed materials combine to restore life to a once-barren space.

cousin of design/build that means the contractor is liable for the project and has to build it for a fixed bid price. That price was a carved-in-stone $8 million.

In 2006, Stoltz recalls, prices of construction materials went totally haywire. The original four-story building became three, and the landscape, as so often happens, was suddenly deferred. "Somewhere between design development and construction documents," remembers Briggs, "it was revealed to us that the landscape had no budget."

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