If I had to rank from most favorite to least all gardening tasks, distributing water from a hose would come in dead last. Rain barrels caught my attention a long time ago because they offer the opportunity to store water where its needed without too much assistance from a hose.
I started with a converted garbage can (bad idea). Then came an old compost barrel. Eventually, Santa Claus delivered two rain barrels one December morning. Then we added rain diverters to some downspouts. Finally, my rain barrel operation was in business and it has been most helpful!
Though these devices seem simple, there are a few things you need to know. Otherwise, you may be like me and wind up reinventing your water collection operations a few times before you feel as though you got it right.
How to Select a Rain Barrel
There are four primary features you’ll want to consider: size, material, the lid and intake openings, and water distribution.
How Big a Barrel?
Say you have a 10 x 10 garden or 100 square feet. During the growing season, assume it will require the oft-quoted inch of rain per week. One inch of rain on 100 square feet of garden is about 62 gallons. (See the sidebar titled “How Much Water?” on this page.) A 60-gallon rain barrel would meet the need of that 10 x 10 garden for one rainless week.
But how much water can be saved from the roof? Say it rains one inch in a week. If you have a 1000-square-foot roof (25’ x 25’) draining into your rain barrel, that inch of rain will provide more than 600 gallons of water, much more than you can hold in a 60-gallon barrel. Enter the overflow hose, a hookup that allows spillover into a connected second barrel. Now you have 120 gallons – enough to last you for two weeks.
Use the rough calculations above and in the sidebar to estimate your watering needs. My recommendation, based on experience with four rain barrels, is to get the biggest you can afford and fit into the available space.
Recommended Materials for Rain Barrels
According to most of the sources I've used, three features of the material should concern you: (1) type of plastic, (2) UV stabilization, and (3) color.
Is it made of food-grade plastic? Many rain barrels are recycled food barrels that once contained juice, pickles, olives, and other comestibles. Once the barrels finish their food storage days, they are safe for rainwater collection.
If you’ve been following the news about plastics and microwaves, you may have read that all plastics leach some chemicals into the materials they contact. This is particularly true of PVC (polyvinyl chloride) and polystyrene plastics when they are heated. PVC plastics carry the recycling number 3; polystyrene is number 6. If you create a do-it-yourself barrel, avoid PVC plastics (recycling number 3) and polystyrene (number 6).
Is it UV stabilized? Plastic ages in sunlight and heat, becoming discolored and more brittle with time. UV stabilizers lengthen life and improve the appearance of your rain barrels.
Is it the right color? Almost any color will do – if it’s not black or white. During the height of summer, when you need water the most, black plastic can retain too much heat. Hot water on a hot summer day can cook your plants. For this reason, homemade barrels of black plastic garbage cans are a bad idea. On the other hand, white plastic food buckets are common and readily available but they’re not opaque. Within a week, you can get quite a lot of algae in a white bucket.
Rain Barrel Lid and Intake Openings
The lid is arguably the most important aspect of your purchase, for several good reasons.
Safety: Rain barrels have some hidden dangers. They MUST be covered at all times. Children, pets, and backyard wildlife may be attracted to them, fall in and not be able to get out. (Last year, for instance, a local squirrel went for his last swim in one of my rain barrels when I left it uncovered for just a few hours.)
Some rain barrels are permanently sealed and have only a screened, louvered 6” opening for water intake. There is one safety disadvantage to sealed models. The filled barrel is very heavy. A person or pet could be knocked over and injured by the weight of a full rain barrel, should it tumble.
Others have a solid screw-on lid with an opening. As for safety, a barrel with a screw-on lid is more likely to spill its water quickly in a tumble. Someone standing nearby might get wet, but probably not hurt.
Some barrels have screen lids. I don’t recommend screen openings, as they may be too weak to withstand the weight of a pet or a curious child’s hands. Screen also admits a lot of algae-producing light.
Mosquito prevention: No one wants their rain barrels to become mosquito nurseries, but it can happen. Mosquitoes, including the Culex mosquito that carries West Nile Virus, will breed in a barrel. The lid is the first line of defense. The sealed, solid lid with a screened, louvered opening is arguably the most effective mosquito screen, followed by screw-on tops with small, screened openings. A few drops of dish soap or olive oil will keep the water surface unfriendly to mosquitoes, as will mosquito dunks containing Bt. None of these harm vegetables.
Cleanliness of rainwater: A good lid can keep small particles and bird droppings out. If it has not rained in a long time, you may want to avoid collecting the first flush of rain. Allow the rain to give the roof a good wash, then open up the downspout diverters and collect away!
The bottom line on lids: Careful choice can make a lot of difference in your ultimate satisfaction.
Rain Barrel Water Distribution
There are two features to understand in water distribution: barrel height and overflow.
Most barrels come equipped with an outlet near the bottom and a short hose. Manufacturers offer both brass and plastic fittings. (Brass is potentially longer lived.) You can certainly add hose length, but the farther your garden is from your barrel, the higher you’ll want to station it. This is especially true if you’re going to use it with a soaker hose or a sprinkler. In my experience, barrels must be at least 12” above ground.
According to Sky Juice New England, a 75-gallon barrel placed 24” above ground level can create enough pressure to operate a low flow hose.
What about overflow? A good rain quickly fills a barrel, so you should only consider models with overflow valves and hoses. These allow you to divert the overflow away from your house, or link another barrel to the first. Otherwise, water can pool up around the base of your foundation – an obvious drawback.
Conclusions
Helpful as they are, rain barrels are only one element of water management during long dry spells. Look at what happens during a 12-week drought: Your 10 x 10 bed theoretically needs 744 gallons over 12 weeks – the contents of ten 80-gallon rain barrels. Under these extreme conditions, rainwater collection is not likely to be the sole solution. Other strategies include drought-tolerant plant selections, 2” – 4” of mulch, and watering only in the early morning. If you have a sprinkler system, be sure to equip it with a water sensor.
Rain barrels can be great garden helpers, especially when you keep in mind the topics discussed here as you select and install your system.
For more information or to purchase rain barrels in southern New England: