Harvested Rainwater in Nogales, Sonora Can Augment Supplies
School project installed but more could be done

To provide water to a revegetation project in Nogales, Sonora, a University of Arizona research specialist worked with teachers and parents to plan and install a demonstration rainwater catchment system at an elementary school. This was thought to be the first such system to be installed in the Mexican city.

(Rainwater runoff is routinely captured in colonias in Nogales since such areas are not connected to city services, but is usually arranged in a makeshift manner, often without sanitary safeguards. For example, contaminated barrels have been used to store water.)

Terry Sprouse of the UA Water Resources Research Center began by conducting a water catchment orientation session for teachers and parents of the Covarrubias Elementary School in Nogales, with both theory and practical application covered. Parents and teachers were invited to participate in the construction of the system. Along with watering a revegetated area, the school’s catchment system also demonstrates a strategy for conserving traditionally “lost” water. The catchment system is part of the Nogales Revegetation Project coordinated by the UA Bureau of Applied Research in Anthropology.

Rainwater collection system at Covarrubias Elementary School, Nogalas, Sonora

Lee Anderson, a Tucson rainwater and greywater re-use expert, designed the system and supervised its construction, with help from school parents. The catchment system is designed to capture water from the roof of the school’s administration/classroom building and store it in barrels, for later use on plants located on the school grounds. With runoff collected from a 1,080 square-foot section of roof, a one-inch rainfall could result in 1,000 gallons of water captured and stored.

The approximately 20,000 square feet of roof at the school could potentially yield 20,000 gallons of water for each one-inch rainfall. The average annual rainfall in Nogales, Sonora is 18 inches. If that rainfall were captured, the result would be 360,000 gallons of water for use at the school.

When viewed in the larger, community-wide picture the water-saving potential becomes more evident. Most of the runoff from the school drains into the Nogales Wash, along with runoff from the city’s downtown area, with the accumulated flow crossing the border into Arizona. Approximately 200,000 people live in Nogales, Sonora. Only 39 percent of the population receive water 24 hours a day, while 36 percent of the population are not connected to the water system. A concerted city water catchment effort could save enough lost water to increase daily water supplies to those already receiving water or extend service to the 36 percent not receiving water.

If only ten percent of the population captured and stored the rainfall on their roofs approximately 600 million gallons (2,000 acre-feet) per year of water would be saved. This is over 11 percent of the total annual potable water-use for Nogales, Sonora.

Sprouse’s work, however, demonstrates some problems with achieving this potential. For example, the materials needed for rainwater catchment systems are not readily available in Nogales, Sonora, and Mexican participants in the project said they would need to get them in Arizona. Also conservation is not a high water priority in Nogales, Sonora. Looking to basins south of the city to satisfy water needs officials may not provide the leadership needed to encourage water catchment.

The City of Nogales, Sonora presently consumes 18,500 acre-feet of water for municipal use per year, while its sister city in Arizona consumes 4,300 acre-feet for the same purpose. Both cities pump water from Upper Santa Cruz River aquifer, which is shallow near the border and sensitive to drought. The water supplies in both cities are vulnerable to water shortages during times of even short-term drought. Recent studies show that long-term drought would greatly exacerbate existing water management problems in the border communities.

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