How Rain Barrels Work

A very crude rain barrel catching the rainwater from the spout. See more green living pictures.
A very crude rain barrel catching the rainwater from the spout. See more green living pictures.
Photo courtesy of Martin Bowker/

­We have evidence that collecting rainwater in cisterns was a common practice in the Middle East more than 4,000 years ago, and its origins probably go back much farther than that. In arid climates, or on islands like Gibraltar that lack river systems, trapping and storing large volumes of rainwater is a practical necessity, and the popularity of this relatively pure source of water is growing -- again [source: Gerston]. At a time when many municipal water districts are experiencing water shortages and consumers are being hit with higher water and sewage bills, the benefits of free water falling­ from the sky are more attractive than they have been in decades. Once a common feature in yards and farms across the United States, rain barrels are experiencing a renaissance.

Rain barrels are containers designed to trap and store rainwater. They can be huge, complex systems that use pumps and linked barrels for storage, or single plastic or wooden drums that catch rainwater swirling along roof gutters and out of downspouts.


­Harvesting rainwater makes good sense. It doesn't contain the dissolved minerals and salts typically found in the well water you might be using to supplement your outdoor water needs. It's safe -- if you follow a few precautions -- and rain barrels are easy to make and install. Using rain­water also helps the environment. Need more encouragement for installing your own rain barrel? In Germany and Japan, there are monetary incentives for rainwater harvesting; Arizona and California also have programs available.

Rain is a good source of water that would otherwise become polluted runoff picking up chemicals and other dangerous waste as it carom­s down streets and gutters on its way to a network of storm drains or the nearest low-lying body of water. In many areas, rainwater harvested from the roof of an average home can go a long way toward providing the water needed to maintain a vegetable garden or your home's landscaping over the summer months.

Intrigued? In the next section, we'll talk about some of the surprising advantages of rainwater.

The Advantages of Using Rainwater

Rainwater is perfect for watering your plants, flowers and grass. You can also use it to wash your car.
Rainwater is perfect for watering your plants, flowers and grass. You can also use it to wash your car.
Photo courtesy of David Cannings-Bushell/

­Rainwater is relatively pure stuff. The process of evaporation leaves chemicals behind, and what you see falling from the clouds starts out pretty clean. It picks up particulates, pollution, pollen and dust as it makes its way to the ground, but even those contaminants become less of an issue if it's been raining for a while and the air is cleaned with a good water scrubbing.

Evaporation is nature's distillation process, and the fresh water you're drinking out of the faucet was a raindrop at some time -- maybe a number of times -- in its long history on the planet. It's true that tap water has been treated with chlorine and other chemicals to make it safe to drink, but for nondrinking uses, rainwater is a good, wholesom­e choice.


Besides being natural, rainwater is usually soft, which makes it a good option for watering your flowers and plants. Actually, the absence of those very chemicals that make tap water safe for drinking makes rainwater a better choice for your outdoor watering needs.

Supplementing your water needs with rainwater will reduce your utility bills, at least during the summer months. It will also reduce the drain on groundwater resources. As communities grow, the demand for water can outstrip the supply. Municipal water districts often rely on groundwater or aquifers that can become overtaxed. Supplementing our collective water needs with a little rainwater can help postpone the costly expansion of water treatment facilities groaning under the weight of population growth, an aging infrastructure and urban sprawl.

In some areas, using rainwater may mean the difference between keeping your lawn and plants alive or watching them die of thirst. In times of drought, when there are restrictions on water use, rainwater may be the only available source of water for landscaping and washing the family car. It may come down to a choice between rainwater and no water at all.

Reducing the demand for water helps protect the local ecology, too. Water that isn't being diverted into municipal water systems stays in the lakes and river­s to sustain fish, birds and other wildlife. Besides relaxing some of the demand on existing water resources, harvesting rainwater reduces the amount of polluted rainwater runoff. Dirty rainwater is often released from storm drains directly into lakes and streams, causing big problems for plants and animals. Imagine the chemical stew you see on the roadways, like oil and antifreeze, washing directly into your favorite brook or creek.

In the next section, we'll take a closer look at how much water you can expect to harvest from your down spouts.

Water Harvesting

A rain barrel can cos­t as little as $20.00 to make, or it can involve a sophisticated system of pumps and tanks that can run into thousands of dollars. Luckily, raindrops add up quickly, so you don't have to make a major investment to reap the benefits of capturing rainwater from the roof of your home. Let's take a look at a few numbers. One inch (2.54 centimeters) of rain falling on a 1,000 square foot (93 square meter) roof will yield 600 gallons of water (about 2,271 liters) [source: Healthy Landscapes]. That's quite a bit of water. The roof itself is your water catchment area, and the water running from your roof down your gutters is fed directly to your rain barrel.

How much can you expect to harvest from your roof? This simple formula will help you figure your potential yield, less any water you may lose from evaporation or spills:


  1. Measure the exterior length and width of your home, plus any roof overhang.
  2. Now multiply the two measurements together. A house that's 30 feet by 40 feet (around 9 by 12 meters) will have 1,200 square feet (almost 111.5 square meters) of roof catchment area.
  3. Now, multiply 1,200 by 0.6, the portion of a gallon that will be harvested by one inch of water falling on one square foot (0.09 square meter) of your roof's surface.
  4. Your 1,200 square foot roof catchment area will yield 720 gallons (a little more than 2,725 liters) of water from one inch (2.54 centimeters) of rainfall (30 x 40 = 1200 x .6).

That's pretty impressive. If you take a look at the difference in your water bills between the summer and winter months, you can start to understand how capturing rainwater can save you money. The average American household uses 30 percent of its total water for outdoor applications [source: EPA].

In the next section, we'll talk about what you need to consider when installing a rain barrel.

Choosing a Rain Barrel


­There are things to consider before installing a rain barrel. Because the rainwater you plan on harvesting is running off your roof, ther­e are safety concerns. Some roofing materials will contaminate rainwater and make it dangerous to use. You should not use roof catchment areas that incorporate asbestos shingles, tar and gravel, or treated cedar shakes. You should also check your gutters to make sure that they don't use lead solder or lead based paints.


Once you know that you can harvest rainwater safely, you need to evaluate how much water you want to capture, and how you want your system to look. Although there are many different styles and designs available, a large aboveground system will take up quite a bit of space in your flowerbed and can get expensive, so it's important to understand what you want and have a budget in mind before you go shopping. You should ask yourself if you plan on watering your lawn, washing your car or maintaining your vegetable garden with your rainwater reserves. Activities like watering the lawn can consume lots of water, so do your homework. Check your water bills from last few summers to determine how much water you use during the peak summer months and plan from there.

Any system you select or build will need a tight-fitting lid to keep animals out and discourage the development of algae. It should also be made of quality material like food grade plastic that's UV protected and have a fine mesh screen to reduce the amount of debris in the water and keep mosquitoes from using the standing water as a breeding ground.

To keep the foundation of your home safe from water damage, it's important that your rain barrel have an automatic overflow mechanism that diverts water back into the downspout once the barrel has been filled or to an overflow hose that drains downhill away from your home.

Other considerations for convenience a­nd water quality are water filtration systems, UV lights to kill bacteria and pumps to make water distribution easier. There are also special diverters available that will block the initial water flow in a rainstorm from going into the rain barrel. After the initial flow washes the dirt out of the air and off the roof, the diverter reroutes water back into the barrel.

Next up, we'll take a look at how to use a rain barrel.

Using a Rain Barrel

This rain barrel is a little bit fancier and a little bit more decorative; you can see the spigot where the water comes out at the bottom.
This rain barrel is a little bit fancier and a little bit more decorative; you can see the spigot where the water comes out at the bottom.
Photo courtesy of RonTech2000/

­Now that you have a free source of extra water, what do you do with it? Even though rainwater is natural, it isn't safe for drinking unless it's been filtered and treated. All that rainwater washing off your roof is carrying pollution with it. This includes particulates from car exhaust and manufacturing smoke stacks, not to mention bird droppings and parts of dead bugs. It's still great water, though; plants love it. You can water the lawn and flowerbeds with it, clean off your siding and hose down the driveway. It's great for washing the car, too.

You can also use it to water your thirsty vegetables, but not in the same way as you would with tap water. When watering your veggies with rainwater, keep the water flow at ground level, away from the stuff you'll actually be eating, and don't use rainwater within a couple of days of harvesting your crop. After harvesting, always wash your vegetables thoroughly with tap water.


There are some good habits you should adopt when using a rain barrel. Keep the top firmly in place. Exposing rainwater to sunlight and open air will encourage algae growth. Make sure the screen is secure to keep out water-loving bugs, like mosquitoes. Clean the filter regularly according to the manufacturer's directions, and inspect your rain barrel every once in a while for leaks. Keep your roof gutters clean, and make sure that water is flowing freely to and through the downspout when it rains.

If you live in­ an area with freezing winters, don't forget to move your rain barrel to a safe location so it doesn't freeze and crack over the winter. It may be necessary to replace part or all of the downspout to adapt it for use without the rain barrel attached. Remember, it's important to be sure that the downspout is working properly at all times to ensure that water isn't pooling too close to your home's foundation.

Next, we'll show you how to make a very simple rain barrel.

Make Your Own Simple Rain Barrel

You can make your own rain barrel inexpensively with a clean, plastic barrel, a downspout extender, spigot, hose, overflow adapter, drill, tin snips, tubing and hose clamps. This bare bones setup will catch and hold water, but it won't have the features of the more sophisticated homemade or prefabricated styles.

  • Select a barrel made of sturdy plastic. Food grade plastic that's UV-protected is the best choice, but any watertight container that's clean and won't rust will work. A good rain will fill a 55-gallon (208-liter) barrel in a few minutes, so it won't take long to fill even a large container.
  • You'll need to place your rain barrel on a level surface next to a downspout. After the area has been cleared, put a platform in place, like cinder blocks or pavers that will keep the barrel off the ground. When it's filled with water, the barrel will be heavy, so give it a sturdy foundation. Adding a little extra height is a good idea, too -- It will help the water to flow better.
  • Drill two holes in your barrel, one 3 inches (7.62 centimeters) from the bottom of the barrel to accommodate a spigot and another hole a few inches (several centimeters) from the top of the barrel to attach an overflow adapter.
  • Screw the spigot into the predrilled hole. Insert the overflow adapter into the hole at the top of the barrel. It should be a tight fit. Attach a length of hose to the adapter and use a hose clamp to anchor it in place. The hose should be long enough to extend downhill away from your home's foundation.
  • Measure the height of the barrel and cut or disconnect the downspout a few inches above it. Some segmented downspouts can be disassembled. If yours has to be cut, you may be able to use tin snips. (If not, you may have to resort to removing the downspout completely and cutting it with a hacksaw.)
  • Attach a flexible downspout extender from the end of the shortened downspout to the rain barrel. Cut a hole in the top of the barrel large enough to accommodate the extender. Slip the extender through the opening in the lid and attach the lid to the barrel. To filter the water entering the barrel, you can attach a plastic mesh bag to the end of the downspout extender and hold it in place with a rubber band. If you do this, be sure to clean the makeshift filter frequently to keep it from clogging.

Take a look at the next page where we'll explore more water and garden related topics.


Lots More Information

Related HowStuffWorks Articles

More Great Links


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