By Sharon Omahen
University of Georgia
When summer arrives, gardeners will wish they could have saved
some of the rain that ran down their driveways this spring. A
University of Georgia scientist is studying ways people can do
just that.
“The greatest demand for outdoor water use in Georgia occurs
during our state’s hottest, driest months,” said Rose Mary
Seymour, a UGA agricultural engineer.
Irrigation water in high demand
“Outdoor use is a major component of the total water demand for
urban areas of our state,” she said. “But in times of drought and
water restrictions, landscape irrigation will most likely be a
low priority for potable water supplies.”
Seymour, a researcher in the UGA College of Agricultural and
Environmental Sciences, has found that using rainwater can reduce
the amount of drinkable water used for irrigation.
“Captured rainwater is of suitable quality to be used for
irrigation if the rain falls on relatively clean, impermeable
areas,” she said. “Collecting rainwater in a retention area also
helps remove nutrients and other pollutants and recharges the
groundwater.”
Seymour’s studies highlight two rainwater collection methods.
One, often called rain harvesting, collects rainwater in a
cistern, tank or pond. The other involves installing a rain
garden or bioretention area in your landscape.
Save for future use
Rain-harvesting systems most often collect rainwater in a storage
tank, either above or below the ground. A pumping system can
supply an automated irrigation system, but the water must be
filtered. Or the rainwater can be siphoned from the tank and
applied by hand.
Unlike gray water, or wastewater from clothes washers, showers,
etc., collecting and applying rainwater doesn’t require special
plumbing codes, Seymour said. It doesn’t contain the detergents
and chemicals found in gray water.
The catch is that rain harvesting systems are best when they’re
designed and installed in a new building, Seymour said. “Usually,
retrofit rain harvesting systems are more expensive and may not
fit well with the existing overall site design,” she said.
Rain-harvesting systems add some costs over using municipal water
alone for irrigation. But Seymour said landscape designers need
to be forward-thinking.
“If municipal water costs continue to rise and water utilities
set up conservation fee structures, the payback period for
rainwater harvesting could be shortened,” she said.
Route rain into garden
Rain gardens and bioretention areas are other options.
“These are both intentional low areas where runoff water from
impervious surfaces is diverted and contained so the runoff will
infiltrate the soil,” Seymour said.
Rain gardens are most often used in home or other small-scale
landscapes, she said. Using plants that fare well in wet and dry
extremes, these gardens create a more natural flow. They keep
rainwater in the landscape, rather than letting it run into
streets and storm drains.
“A rain garden catches the runoff water from a particular
impervious area such as a rooftop, patio, driveway or parking
area,” Seymour said.
Ideally, water shouldn’t stand in a rain garden more than 48
hours after the rain stops. Since it isn’t standing water,
mosquito breeding isn’t a problem.
Don’t install rain gardens over the drain field of septic systems
or next to building foundations.
Bioretention areas serve a similar function, but tend to be part
of large, commercial landscapes. They collect rainwater from
large roofs and parking lots.
Can’t pick? Use both
Large businesses can combine rain harvesting tanks, bioretention
areas and rain gardens, Seymour said.
“Creating a rain garden downstream from the overflow of a rain
harvesting system can be an even better on-site storm-water-
reduction system than either independent method,” she said.
“No matter which system you choose,” she said, “using rainwater
to reduce the use of potable water on landscapes is a win-win
strategy for both commercial and residential landscapes.”
