Throwing a rain barrel in here or there used to be a nice-to-have for many gardeners. But as we experience more unpredictable weather patterns (including heavy flooding and more periods of drought) rainwater collection systems are rapidly moving to the need-to-have category.
Replacing standard hoses and sprinklers with spot watering and drip irrigation is also gaining ground. Harvesting rainwater—particularly during extremely heavy rains—reduces stormwater runoff, thereby protecting area watersheds.
It also mitigates topsoil and nutrient loss from your own land.
Mary Ann Capehart serves as instructional specialist for Water Wise, a program within the University of Arizona Cooperative Extension service. According to Capehart, rainwater is particularly prized for its ability to help flush salts out of the soil.
“Groundwater—especially in the West—tends to have high salinity,” she says. Because its naturally high mineral content can make nutrient uptake more difficult for plants, even an occasional watering with rainwater can make a big difference.
Gardeners making the switch from municipal water sources to rainwater may notice their plants perking up, too. Some municipal water supplies may contain chemical disinfection byproducts.
“Chlorine evaporates, but chloramine does not,” Capehart says. “And more water treatment plants are turning to chloramine.”
Municipal water also can contain emerging contaminants such as pharmaceuticals, microbeads from personal care products, fertilizers, herbicides and pesticides.
“Plants respond a lot better to rainwater,” says Jonathan Meier, owner of Rain Brothers, a company in Columbus, Ohio, that specialize in sales and service of everything related to cisterns. “And a small-scale rainwater collection system will pay for itself within a season typically—especially if someone is on municipal water.”
Meier began selling rain catchment equipment in 2007, and he says 2020 was his best year so far. “People were stuck at home and thinking more about backyard conservation or backyard gardens,” he says.
Sarah Sojka, vice president of the American Rainwater Catchment Systems Association Foundation board and an associate professor of environmental studies and physics at Randolph College, has noticed an uptick in interest in rainwater collection, too. “We’ve seen increases in people coming to the [ARCSA] website,” she says.
“It is actually really hard to track how many rainwater harvesting systems there are out there, particularly because they range so dramatically in size from a 100-gallon barrel to 1-million-gallon, underground storage system, or a 1- or 2-million-gallon pond.”
What’s Your Capacity?
If you are in the western U.S., you might already rely on a rain catchment system, but you may need to switch to even larger tank in the coming years. “Normally, we would have a giant monsoon, and you would get as much [rainwater] as you could that one time of year and then save it for the really dry spells,” Capehart says.
“[However,] we are losing rainfall altogether, so [when it does rain,] it’s like, ‘Ooh! How much can I harvest?’”
Whether you have a modest rain barrel and want to upgrade or you’re starting from scratch, you can follow a simple formula to find out what will work best for your needs.
“It’s a balance between your roof size — because you’re not going to be able to capture more than what hits that roof in a given period of time — and how much water you actually use,” Capehart says.
“The engineering formula for stormwater calculations is 0.6 gallons per square foot of roof,” Meier says. In other words: If, for instance, your roof area is 1,000 square feet, you would multiply that by 0.6 gallons. If you get an inch of rain, you could collect 600 gallons of rainwater from a roof that size.
Next, determine the amount of rainwater you’re likely to use. “If I am watering this much area, and I only have a 55-gallon drum, how effective is that going to be?” Sojka asks.
If you already have an established garden, you can assess your water usage with a hose meter. “They’re not expensive, and then you can see how much you’re watering,” Capehart says. “Water by hand [with the metered hose], see how much water your plants need, and then you can think, ‘If I was doing this every week or even more during the hot periods, what would that look like?’”
While individual rain barrels hold about 55 gallons each, larger, aboveground tanks can accommodate 500 gallons or more. “When you think about how much you might want [in order] to water a tree in a drought, for instance, it would be something like 1,000 gallons,” Capehart says.
If you get frequent rains, you might not need a behemoth storage tank. But if rain is scarce, it’s better to capture as much as you can while you have the chance.
Rainwater Collection Caveats
Before you spend a dime on barrels, tanks or cisterns, check in with your county extension agency or water resource board to make sure you’re legally allowed to harvest rainwater where you live.
“One of the things that’s challenging with rainwater harvesting is that it’s regulated by so many different people,” Sojka says. “It’s regulated on the water rights side. It’s regulated on a health side. Sometimes, it’s regulated on a stormwater runoff side.”
Let’s say you’ve secured the all-clear and you think you’ve got the numbers and sizes of your catchment tanks all figured out. That’s a good start, but it’s just the start. “The top mistake I see people making is selecting the wrong downspout to harvest from,” Meier says. “Just because you have a downspout on the house doesn’t mean that you have a lot of water coming off of it.”
He recommends locating the largest area of your roof that’s being drained and harvesting from that particular spout. Also, be sure the pipes that go from the roof gutter to your rain barrel are large enough to capture even very heavy flows.
You should also take care to divert your barrel’s overflow well away from your home’s foundation. “We have to think about what happens with failure,” Sojka says. “What happens if the little spigot at the bottom of your rainwater container starts leaking? Where is that leak going to go?”
Something else to consider? “A lot of people put in a system of rain barrels and they’re like, ‘Oh, I’m just going to fill the watering can over here and I’ll carry it over to my garden and it will be no big deal,’ Sojka says. “But within a month of doing that, they’re like, ‘I’m just going to use the hose, because this is a pain.’”
To get good use from your collection system, you may want to incorporate a small pump or elevate your barrels in order to increase your potential water pressure.
“We recommend a 2-foot elevation on the barrel,” Meier says. “That will give a little bit of water pressure, but it’ll also make that water higher, so that it can flow better to the spots you’re trying to water.”
Still, don’t expect to use just any standard drip irrigation hose with this setup. “Most drip irrigation needs at least 20 psi, and you’re not going to get that from a lot of smaller rain tanks,” Capehart says. “But there are things that you can use that are very low psi like certain irrigating tapes.”
Some rainwater collection equipment suppliers also sell low-pressure emitters to be used with gravity-fed rain barrels.
Incorporating a drip system is a much more efficient use of water. “You will extend the duration that you can use your rain barrel, and, because [the drip system] waters slowly, the roots of the plants have a longer time to absorb moisture,” Meier says.
If you do choose to use a specialty drip hose or irrigating tape, watch for sediment build-up. “Drip hoses can clog pretty easily, if you are not careful about water quality,” Sojka says.
Keep It Clean
Your rainwater quality partly depends on the degree to which you maintain your catchment system. “Rain is pretty clean — especially if you do some prefiltration before it hits the tank,” Capehart says. At minimum, that means keeping roof gutters clean and free of leaves, sticks and other debris.
If possible, you should also keep your tank in the shade. This will help to reduce or eliminate algae growth in your rainwater storage containers. (And, in the case of plastic catchment systems, the less exposure to plastic-degrading UV rays, the better.)
Rainwater collection systems should also be mosquito-tight. “Make sure that you have sealed the openings with netting to prevent mosquito breeding,” Sojka says. “All of these are things that people need to think about, and they are not particularly hard. But it is a little more than just cutting off a gutter and dumping it into a barrel.”
Once you have your system dialed in, rain harvesting can be downright fun. “A really cool byproduct of rain harvesting is how you stay in closer contact with the seasons, the rainfall and the cycles of rain,” Capehart admits. “That does make it very exciting when it rains. And it is really high-quality water.”
This article originally appeared in the July/August 2021 issue of Hobby Farms magazine.