Alternative: Possibly drinking treated sewage
A precious natural resource many Tucsonans let trickle away could mean big savings.
Harvested rainwater could be used to offset drinkable water now pumped, treated, delivered and used outdoors, said James J. Riley, associate professor of soil, water and environmental science at the University of Arizona.
An increase in rainwater harvesting could make it unnecessary to secure new, expensive and less desirable sources of water as the area’s water needs grow, he said.
“If you could save the requirement of having to provide extra water by using rainwater, you could save a lot of installation costs, meters and piping to provide that source of water,” he said. “You could really reduce what it would cost.
“If you use the water that falls on your property and roof for irrigating, we can save a lot of the groundwater we are pumping,” he said. “We could save enough so that it might not be necessary to treat sewage to potable water quality standards in the future.”
Riley will offer the public tips on getting involved in rainwater harvesting at Tuesday night’s free UA Flandrau Science Center science cafe event.
Following Riley’s “Harvesting the Sky – Rainwater, an Important Source of Water for Tucson” presentation, an informal discussion on rainwater harvesting will take place.
Outdoor uses account for about 45 percent of the water used at the typical single-family home here, said Fernando Molina, conservation manager of Tucson Water.
About 35 percent of area commercial/industrial water use is outdoors, and about 26 percent of multifamily housing, or apartment, water use here is outdoors, Molina said.
“We do view water harvesting as a component to reducing demand in the long run,” Molina said. He added that it would be difficult to get enough participation to attain levels that would do away with the need to expand the water system to meet future needs.
A Tucson ordinance passed in October that requires rainfall to make up half the water used on commercial landscaping is a step in the right direction, Molina said.
Riley applauded the ordinance, which takes effect in June 2010 and applies to new developments.
Requiring new homes to be fitted to capture and use rainfall could also have a big impact, Riley said.
No Tucson residential requirement to harvest rainfall is in the works at this time, Molina said.
Riley said he and students in his UA water harvesting class studied 20 one-square-mile areas in Tucson, and found that the annual rainfall total equalled about 75 percent of the potable water the city was bringing in to the sites analyzed.
Riley could not say what percent of water used by the average household could come from harvested rainwater – or how much money could be saved.
Much of the rainfall is being wasted, running off properties into streets and arroyos, he said.
Rainwater harvesting could also cut down on flooding after storms, he said.
He proposes directing the rainfall to water plants, or to cisterns for storage, to utilize the resource that is precious in the desert.
Rainwater harvesting should not just be considered conservation, but rather a component – along with groundwater, Central Arizona Project water and other reclaimed sources – for providing the area’s water needs, Riley said.
Riley and his students have worked with the UA Surface Water Working Group, facilities management, community relations office and members of the community to design and build rainwater harvesting systems at several sites around the UA campus.
One example is the UA Visitor Center at 811 N. Euclid Ave.
Gutters ringing the roof’s edges collect rainwater and send it to downspouts that direct the water to landscaped plant beds.
An estimated 100 tons of soil were moved to form large sunken areas where water is directed to plants.
These valleys at the visitor center have plants requiring less water higher up, and plants needing more water are located in the lower riparian areas, he said.
The Visitor Center parking lot is set up to drain to one end, where rainfall is channeled to water plants in a valley area dug out behind the building.
Roof gutters also drain to two large metal cisterns, which are now filled to near their combined 2,500 gallon capacity, he said.
Other rainwater harvesting projects have been installed at UA’s Aerospace & Mechanical Engineering, Meinel Optical Sciences and Family & Consumer Sciences buildings and Cochise residence hall, he said.
Another project is at work collecting rainwater at a housing area at UA’s Biosphere 2 near Oracle, he said.
IF YOU GO
• What: University of Arizona Flandrau Science Center science cafe event
• When: 6-7:30 p.m. Tuesday
• Where: Cushing Street Bar & Restaurant, 198 W. Cushing St.
• Topic: “Harvesting the Sky – Rainwater, an Important Source of Water for Tucson”
• Presenter: James J. Riley, associate professor, University of Arizona department of soil, water & environmental science
• Cost: Free, with food and beverages available for purchase
TO GET STARTED
People who want to get started harvesting rainwater should keep it simple, said Professor James J. Riley. “This is not rocket science,” he said.
“Start small. Once people get the fever, they begin to think too big,” he said. “Get started on small things and see how that works.”
A good first step is revising landscaping to better utilize rain to water plants on your property. Locate plants in sculpted depressions rather than on hilltops, and use berms and ditches to channel rainwater water to plant beds instead of running into the street, he said.
“You want the sidewalk to be above the soil level,” he said.
Some people opt to use a rain barrel or cistern to collect water for later use.
Water stored from the winter rains can keep plants flourishing in the dry months of April, May and June before the summer monsoon hits, he said.
“Now is the crucial time,” he said. “You want to be collecting now so that by the end of March your cistern is nearly full to get through the dry months.”
People don’t have to spend big bucks on a huge cistern to store water from the roof unless they really need the capacity, he said.
“Decide what you are going to do with this water. It is not enough to have a tank full of water,” he said. “You need to have a plan on how you are going to use it.”
Directing “grey water” – from sources such as the washing machine rinse cycle – to plants is also a good step, he said.