A Harvest of Rain

The Cubo tank

The Cubo tank

Rick and I arranged to meet at Taco Bell in Tucson. Rick is the owner of Oasis Water Harvesting and on the flat bed trailer behind his truck four polyethylene tanks stood in a variety of earthy colors. The100 gallon Cubo tank I was buying appeared doll-size in comparison to a 1500 gallon monster destined for a medical complex.
The Cubo tucked easily into the back end of the 4-Runner. It came outfitted with a screened top to keep out mosquitoes as well as a spigot and overflow valve. At home I positioned the tank under a scupper that drains a fair portion of our roof.
Now I’m waiting for rain. The monsoon season is upon us and moisture is creeping into the seared air. The tedious expanse of overhead blue is broken by mounds of clouds pierced with sunlight. According to Ed Phillips’ Arizona Almanac, the average rainfall in Phoenix is 7.8 inches. Nearly three inches is normal for the monsoon season, when rain can come down in bucketfuls.
The rainwater that sheets off of homes, surges down driveways and foams like rivers in suburban streets is a valuable commodity. Unlike our local water sources rain is salt free, and carries nitrogen and other beneficial microorganisms necessary for green plants. This precious water can actually be harvested from each and every rooftop.
There’s a formula for this and lots more information on rainwater harvesting online at the University of Arizona Arid Lands Information Center. Figure the square footage of your home by pacing off the dimensions of the exterior. For an impermeable surface such as a roof, one inch of rainfall equals .6 gallons of water for each square foot of roof catchment area.
Including the garage and covered patio, our house provides about 2400 square feet of catchment. This means the house collects 1440 gallons of water when one inch of rain falls. In past monsoon storms (pre Cubo) two scuppers out back gushed water into the yard creating a muddy mess. Much of the water draining off the front of the house dumps onto our paved driveway where it flows downhill, one of many tributaries to temporary rivers rushing through the streets.
These ephemeral streams do not soak into the earth to nourish plants or refill aquifers. They don’t deposit nutritious silt and organic debris to renew the soil. They churn across asphalt rinsing up oils and toxins laid down for months by vehicle traffic. The turbid flows thunder through storm drains to massive treatment plants where the water must be sanitized before it’s useful again.
My 100 gallon tank is just one small step. I’ll water my potted plants and vegetables with what I collect. We also put in a french drain out back, that will channel runoff to a planted area. Gutters may be the solution for the front. In the desert we begin to realize the importance of careful husbandry of the rare water that comes our way.

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One response to “A Harvest of Rain

  1. I could use so many of these….living at the bottom of the hill. I get everyone’s runoff and on a bad storm day my washes overflow and disaster strikes. I need a water catchment gizmo the size of a lake…but a baby step like this might help. Thanks for all the good information.

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