Six things you should know about rainwater harvesting in the desert
Brad Lancaster is an expert in rainwater harvesting and water management in the desert. The Tucson native will be in Las Vegas on June 22 for a water-use workshop sponsored by Great Basin Permaculture.
1. The secret to urban water harvesting is using the many impermeable surfaces that surround us: roofs, streets, sidewalks and driveways. The runoff from those surfaces amounts to a huge amount, if properly collected and used for irrigation.
2. Good collection techniques can triple the amount of water that falls, so for example, the patch of garden that now needs irrigation would get about 12 inches a year. That’s still pretty dry, but it does just lift that patch out of a “desert” definition. Diverting rainfall from your rooftop and driveways can provide quite a bit of water for irrigation. Lancaster suggests sealed, light-proof collection barrels to thwart mosquitoes and evaporation. The water in the collectors — and they have to be pretty big, because even a small area of rooftop collects a lot of water very quickly — can be used for hand-watering or hooked up to a hose.
3. Another part of good rainwater use is designing the landscaping so that water flows into rather than off of it. Most landscaping is planted in mounds — the reverse of what we should be doing. “Instead of a mound, make a bowl-like topography that will hold the water runoff and organic matter,” Lancaster says. Leaves and grass cuttings, instead of going to the dump, will go into the depressions, improving the soil and increasing water infiltration. “About 12-14 percent of the solid-waste stream is yard trimmings. Instead of going to the dump, it should be used on-site to enhance soil fertility.”
4. City officials are learning to love Lancaster’s revolutionary ideas. “In Tucson, the average residential street drains 1.25 million gallons a year, per mile. That’s enough water to irrigate 400 native trees per mile, one tree to every 25 feet. This converts a water-draining street to a water-harvesting street. In Nevada, you would get a third of water we have, but that’s still a significant amount of water. Here in Tucson an ordinance was just passed by the City Council that all new city roads must harvest at a minimum all the water from a half-inch rainstorm. That’s a great beginning.
“They don’t have to worry about leaks, they don’t have a water bill. They’re reducing costs and they have a much more livable, beautiful community. So we get these multiple benefits.”
5. Harvesting rainwater also would take some pressure off of the Colorado River by avoiding the significant evaporative losses that happen in Lake Mead. Also, rate-payers won’t have to pay for the energy used to pump the water up from the lake.
6. The Southern Nevada Water Authority is not a fan of “gray water” or used-water collection, Lancaster notes. (SNWA officials cite a study in Western Australia that showed an uptick in water consumption after homeowners installed gray-water reuse systems.) “So while the local water authority is not promoting gray water, I look forward to having that discussion at the event,” he says. LAUNCE RAKE