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ECOShift Environmental Blog

Jun 19

Rain Barrel Basics - Part 1

Posted by: Geoff Jones

Geoff Jones

One of the most basic and common forms of rainwater harvesting is the Rain Barrel. All over North America ever increasing water demands are putting more and more stress on our water systems. In the summer months the additional demand for water due to irrigation and other outdoor uses is pushing some water treatment facilities, and ground water sources, to their limits.

One very simple, yet effective approach to helping reduce the demand for water is to use a rain barrel. Rain barrels can eliminate the need to use municipal water to maintain a healthy and flourishing garden. Many people invest a significant amount of money and time into shrubs, plants, flowers, vegetables, trees etc. around their homes. Each may have a different purpose (i.e. food, visual appeal, privacy etc.) but to the homeowner they are important parts of their home and lifestyle. By using rain barrels to collect rainwater for irrigation these plants, in most cases, can be sustained with little or no potable water demand depending on the rainfall patterns in your area.

This isn't some new technology or a complicated system. Our parents, grandparents and past civilizations used rainwater. A rainbarrel is a great way to start learning about rainwater harvesting and learning how you can reduce your water demand.

How Much Water Can I Collect?

Although it may not rain everyday, or even every week, you might be surprised by how much water can be captured from your roof during a short, but good rainfall. To calculate the potential water that is captured from your roof during a rain storm you need to know 2 key pieces of information:

1) Area (in sqft) of your roof.
2) Volume of rainfall (in inches) during an average month, or week or single rainfall (depending on what data is available to you).

Once you have this data you can use the formula below to calculate how much rainwater you would capture over a given period of time. Let's look at a simple example below:

A = (catchment area of building) = 1000 sqft
R = (inches of rain) = 1 inch (25mm)
G = (total amount of collected rainwater)

G = A * R * (620 gallons / 1000sqft)

G = 1000 sqft * 1 inch * 0.62

G = 620 Gallons

To convert this to liters just multiply by 3.78. So, with a solid 1 inch rainfall we would capture about 620 gallons, or 620 * 3.78 = approx. 2350 liters of water from a catchment area of 1000 sqft. Said another way; for every inch of rainfall you will capture about 0.62 Gal (2.35L) per sqft of roof surface. Keep in mind that this doesn't take into consideration losses and efficiencies of different roof surfaces but for a rough idea you don't need that level of detail.

Are you surprised? It's really pretty amazing how much water can be collected from your roof.

Now, you don't need to worry about storing all the rainwater every time it rains. The idea is to capture what you need based on your irrigation requirements over a typical period of drought in your area. This is something that you will have to determine based on the number of plants you have and how often they need to be watered etc. It is recommended that your speak to a professional about the appropriate watering patterns for your situation to avoid over or under watering and to ensure maximum benefit from your rainwater collection efforts.

Protecting Your Rainwater

When capturing water it is important to ensure that you have a screen on your barrel to filter out any large contaminants that may come off your roof (i.e. dead bugs, leaves, shingle debris etc.), and even more importantly to protect your water from mosquitoes. Mosquitoes bread and lay their eggs in standing water so a screen should be used to prevent your rainwater from becoming a mosquito paradise. It also deters people or kids from playing in an open barrel and adds some safety to prevent animals etc. from getting in the barrel.

In more advanced systems where rainwater is used for more than just irrigation consideration should be given to pre-filtration systems. We won't focus on these for discussion on a basic rainbarrel system but the purpose of pre-filtration is to reduce contaminants (leaves, debris, animal droppings etc.) that could enter into your tank to help ensure higher water quality where required depending on end use applications. In most cases, for a basic irrigation focused rainwater harvesting system using rainbarrels, this is not necessary.

Stay tuned.

In Part 2 we'll talk a little about layout and drainage and considerations for irrigating your lawn.

Comments (1)add
easier math
written by SJ , July 07, 2009
I found a calculation that is much easier to use - It says for every one square foot of roof, every time it rains one inch that equals about 1/2 gallon of water
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