Water Use Studies

Water authorities in drought plagued areas of the Southwest faced with water shortages have conducted water studies to learn whether water savings, monetary savings and maintenance time savings can be had by installing xeriscape landscapes in place of traditional high water-use turf grass lawns (fescue and bluegrass). These studies require individual residences to sign up for the study and comply with the requirements over a period of 3 to 6 years, depending on the study.

Some water authorities have encountered difficulties in enticing sufficient number of home residences to join the study. Despite this problem, water authorities have determined that water, monetary and maintenance (labor hours) savings can be substantial, with the greatest savings incurred when all seven basic xeriscape principles are implemented.

YARDX Project along the Colorado Front Range

The YARDX (Yield and Reliability Demonstrated in Xeriscape) project was conducted from 1997 – 2002 with nine water utilities along the Colorado Front Range and was comprised of 357 single family landscapes in Arvada/Wheat Ridge, Colorado Springs, Denver, Fort Collins, Greeley and Highlands Ranch. Xeriscapes were compared to control landscapes, both with metered water usage, converting the water data to monthly usage amounts applied per square foot of landscapable area. The focus of the study was to compare water use only during the growing season. The YARDX results indicated a savings from 18 to over 50% of water compared to traditional landscapes. http://www.coloradowaterwise.org/yardx.htm.

Xeriscape Conversion Study, SNWA, Final Report Released in 2005

Residents in the Southern Nevada Water Authority (Las, Vegas, Nevada, etal.) use 59% of the available drinking water, and 70% of this residential water use is for their landscapes – in the summer the water use jumps to 90%. Southern Nevada is in the Mojave Desert.

A study performed by the Southern Nevada Water Authority from 1995 – 2001 (completed report, 2005) determined that landscapes with newly planted xeriphytic plants used 17.2 gallons of water per sq. ft. per year compared to 73.0 gal./sq./ft./yr. for traditional turf grass landscapes. The Xeric Group consisted of 499 properties of at least 500 sq. ft converted to xeric plantings using desert-adapted trees, shrubs, ornamental grasses and mulch with a canopy coverage of at least 50% at maturity. There were 253 residences in the traditional Turf Group averaging 2462 sq. ft. of landscaped area. All test properties had in-ground irrigation systems that were metered and monitored.

The water savings by the Xeric Group translated into an average yearly reduction of 30% of the total household water use, or about 96,000 gallons of water for the average household. Water savings rate varied with mature plantings and density of plantings. (Study findings are available at www.snwa.com/html/land_xeri_study.html.) During the peak water use month of July, xeriscape homeowners would realize a 70% savings on their water bill. This study cited that one of the greatest benefits of xeriscape to utility companies and homeowners, is the drastic moderation of water use during the summer months, avoiding “peaking” that taxes water utilities and often forces restrictions on water usage.

Studies are proving that landscapes of low water-use plants do save on water. The SNWA study figures are averages. Greater savings are obtained with low-density canopy coverage and frequency of irrigation controller adjustments (turning off irrigation systems after rainfall, change of seasons, etc.). Real reduction in water use is an individual effort. Each of us can make a difference, even in a small way. In southern Nevada, for every square foot of turf converted to a low water-use plant area, 55.8 gallons of drinking water are saved each year.

Southern Nevada has a yearly ET (evapotranspiration) water requirement rate of 90 inches, and receives only 4.5 inches of annual precipitation. The best figure I’ve been able to come up with for the Amarillo area is a yearly ET rate of 70 inches, with an average annual rainfall of 17 – 21 inches of precipitation.

Let’s say a homeowner decided to convert the hottest area of their landscape to a xeriscape landscape – the hell strip, or xeristrip, that narrow band between the sidewalk and the street. In southern Nevada, for a xeristrip approximately the size of my xeristrip, 6’ x 40’, or 240 sq. ft., savings in water for just that one homeowner, for just that one area, would be 13,392 gallons per year (240 sq. ft. x 55.8 gallons/sq./ft.).

Naturally, for Amarillo, the water savings per sq. ft. would not be as much as for southern Nevada, but still noteworthy. If water savings per square foot in Amarillo was just 50% (or 6,696 gal./yr. per xeristrip) of the savings in southern Nevada, that would still be a considerable effort in the conservation of water. With only 1000 Panhandle homeowners converting approximately 240 sq. ft. to xeriscape landscaping, almost 7 million gallons of water could be saved yearly. This is just a drop in the bucket of what could be saved, region-wide!

Arizona Study

Another study, this time in Arizona, dramatically points out that an integral component of any low water-use system is the expertise of the operator (that is, knowledge base of the owner-gardener). In 1998, a study began in Phoenix and Tempe, Arizona, to determine whether there was an actual difference between landscape water use and appearance between xeriscape, or drought tolerant plantings, and traditional mesic, or medium to high water plantings. Homeowners agreed to fit their irrigation systems at the backflow preventer with a water meter. They were asked not to change their watering practices. "We found that the average amount of water per area of landscaped surface (including non-vegetated areas of decomposed granite) applied to xeriscapes was higher than mesic plantings." Astounding!

Two homeowners on the same street with similar front-lot sizes in Phoenix were compared. Both had similar xeriphytic plants. There was no measurable difference in plant appearance or fitness, although one homeowner used 218,000 gallons more a year for the front lot (1.2 gallons per square foot per month, vs. 9.9 gallons per square foot per month). Frequently, the study noted, homeowners in the Phoenix and Tempe areas described their landscape preferences as “oasis” rather than desert. This mentality carried over into their watering practices.

The study found that "in central Arizona landscapes, xeriphytic plants are over-watered to stimulate growth and appearance of vigor. Paradoxically, these plants grow rapidly and are then pruned to keep them from 'getting out of control’ . . . Homeowners think their desert plants look too dry, wispy, and gray so they fix this 'problem' by watering more." (Southwest Trees and Turf, March 2000, reprinted in WaterWise, The Newsletter of Xeriscape Colorado, Nov./Dec. 2000) These gardeners failed to cash in on the benefits of a xeriscape landscape: low water use, low maintenance, and monetary savings.

Changes to Gardening Maintenance Needed

Just as we've learned that much more is required to make plants grow in our soils than just adding water, there are more ways to conserve water than just using less of it, but this is important too. Our watering habits are ingrained. When I planted my first xeristrip, I had to remind myself not to water so much; it wasn't necessary. When the temperatures soared above 90°, I was hot and thirsty. My xeric plants were OK. Most plants can withstand additional water (with the exception of drought-requiring plants), but they don't need it.

The Xeriscape Conversion Study by the Southern Nevada Water Authority noted irrigation practices of the xeric gardeners that were monitored. The xeric gardeners watered the turf areas of their landscape below ET rates in the summer, but “considerably higher” (twice) the requirement in the winter. People in the Turf Group, on the other hand, water at 120% ET in the summer and close to ET in the winter months.

Each plant has definite water needs that must be met for survival. There are several factors that determine how much water and how often to supplement them with: air temperature, solar radiation, humidity, wind speed, cloud cover, soil composition, texture and organic content, maturity of the plant and expertise of the home gardener. To be most effective in conserving water, know your plant, know your soil, and pay attention to changes in the weather.

I have to remind myself, when our sun scorches my skin, when summer days grow unceasingly hot, when the unrelenting wind evaporates whatever moisture we do have, my low water-use plants can take it. Under these conditions, our first reaction is to run outside and supply them with a relieving drink. Resist this temptation. Just put the hose down and slowly back away.

Angie Hanna


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