Rain Barrels & Cisterns

Rain barrels and cisterns are some of the earliest water collection systems ever developed. They were routinely used throughout Palestine and Southeast Asia at least 2,000 years ago.

Although modern plumbing has virtually eliminated their need they are enjoying a comeback as part of low impact development (LID) and stormwater BMPs.

In terms of how much water a rain barrel or cistern can collect, the rate is as follows: for every inch of rain that falls on a collection area of 1,200 square feet (e.g., roof with gutters), you would collect approximately 600 gallons of rainwater.

Why bother? Well some folks just don't realize how limited a resource freshwater is in our world but consider the following: more than 70% of the Earth's surface is covered by water, but only 2.5% of this supply is considered freshwater. The rest is found in the form of saltwater in the oceans. Of the freshwater that exists, most is locked up in glaciers and ice caps. Water can also be found in the form of clouds and humidity in the soil. That leaves us 0.3% found in the form of lakes, rivers and streams. Unfortunately, much of this small amount of freshwater is in danger of drying up or becoming so contaminated that it cannot be used for human consumption. Changing our habits of water use can help to abate this growing problem. For more information on world water consumption, you can review this government website.

There are a number of technical features that should be incorporated into any rain barrel setup, which include:

screens on gutters and downspouts to remove sediment and particulates as well as keeping mosquitoes out;
option of draining the system completely for maintenance;
adequate storage capacity; and
water treatment options such as filtration or disinfection

Considering that most of the water used in the average household doesn't require potable water, the use of a cistern can supply water to flush toilets, wash cars, irrigate the lawn, and more. However, their easiest use in stormwater management is simply reducing runoff.

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Cisterns are typically larger installations and more commonly seen with businesses or commercial and industrial applications reflecting the larger sized rooftops and amount of impervious surface/runoff volume.

1500 gallon cistern fed from 2 gable downspouts

Cisterns should be located for easy maintenance or replacement so it's quite common to have large units placed above ground level but underground tanks are also popular.

Individual cisterns can be located beneath each downspout or the entire storage as one large, common unit. Residential use cisterns range from 100 to 1,400 gallons while commercial can accommodate much larger volumes.

If the system is designed for more than just supplemental use, such as full time domestic use, the capacity should be based on a minimum of 30 gallons per day per person.

In fact, a commonly used cistern is a converted septic tank. Once equipped with the proper drainage and pump, it can accommodate some of the same principles but with stormwater instead of sewage.