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Cisterns can be a great way to harvest rainwater and use it on your property!

The first step will be to determine an appropriate site for your cistern.

Cisterns

Photo Credit: ECWA

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In a storm, the majority of runoff comes from impervious surfaces - such as your driveway or the road. Any downspouts that deliver water directly to one of these surfaces are considered 'priority downspouts' and should be re-routed into a cistern if possible.

Cisterns

Photo Credit: Mitch Woodward, NC Cooperative Extension

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The cistern should be placed downslope from your house or building. This is because in an intense rainstorm, your cistern will be designed to overflow - and you don't want that water ending up under your house!

Cisterns

Photo Credit: EcologyAction

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If you must place a cistern upslope from your house, make sure the overflow is routed away from your foundation. If you have any questions, feel free to contact us!

Cisterns

Photo Credit: ECWA

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If you intend to use a cistern to water your garden, the cistern should be placed uphill from the garden site - this allows gravity to do all the work.

If your garden site is uphill from the cistern, you'll need to install a pump to counteract the effects of gravity.

Cisterns

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Now, we need to determine the amount of water that you will expect to use - this is called your 'water demand'.

Cisterns

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The most likely time you'll need to water your garden will be during the summer. Say for instance it doesn't rain for the month of June - you'll still want to be able to water your garden once a week for those four weeks.

Cisterns

Photo Credit: ECWA

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Gardens generally need about an inch of water per week to thrive.

So, take the square footage of the total garden area you'll be watering and multiply it by 0.1 ft (about an inch of water) and 4 (the number of weeks you'll need to water).

Cisterns

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This gives your 'water demand' in cubic feet. To determine the number of gallons you need, take that number and multiply it by a conversion factor of 7.48 gallons/ft3.

Cisterns

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For example, if you need to water 100 ft2 of garden, multiply (100ft2)*(4 weeks)*(0.1ft) to give you 40 ft3 of water, or about 300 gallons, for the month.

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Calculate your own water demand.

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That sounds like a lot of water!
Next, we need to make sure that this about of water can be collected by the cistern during rain events. This is called your 'rain water supply'.

Cisterns

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This calculation is similar to the 'water demand' calculation. For this calculation we'll assume you've just received a 1-inch rainstorm - unless you live in the desert, this should occur at least once a month in your area.

Cisterns

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Take the roof area flowing into the downspout that feeds the cistern, multiply by 0.1 ft of water, and then multiply by the conversion factor of 7.48 gallons/ft3.

Cisterns

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Because not all water that falls on a roof reaches the cistern, we need to factor that in - multiply everything by 0.9 to signify that 10% of the water will be lost.

Cisterns

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For example, assume that the roof area feeding the cistern is 400 ft2.

Calculate (400ft2)*(0.1 ft)*(7.48 gallons/ft3)*(0.9) to find your total water supply of 269.2 gallons per 1-inch rainstorm.

Cisterns

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This means that you'll almost be able to meet your water demand with a single one-inch rainstorm.

Cisterns

Calculate your own water supply:

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In the Piedmont of North Carolina, the average monthly rainfall is between 3-4 inches - more than enough to fill a 300 gallon cistern from a 400 ft2 roof.

Cisterns

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Photo Credit: ECWA

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Now that we have a spot for the cistern that we know will serve your water needs, it's time to install it. The following example uses an (AguaFria) cistern, but many other models can be used!

Cisterns

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First, you'll need the cistern, which you can purchase online or from a local outlet; several bags of paver base; some elbow downspout fittings; PVC fittings, primer, and glue; and 4-8 cinder blocks or large paving stones for elevation. These last two can be purchased from your local hardware store.

Cisterns

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Recommended tools for the project include:

Cisterns

  1. Shovel
  2. Tamper
  3. Saw
  4. Level
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Near the downspout that will feed your cistern, level an area of ground that is slightly larger than the footprint of the cistern itself.

This doesn't have to be exactly level, but should be close. You can prcisely level it during the next step.

Cisterns

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Next, place your paver base across the entire area and tamp it flat.

Paver base is easy to move around so be sure to get the base precisely level during this step.

Cisterns

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After you have a solid, level base, begin placing your cinder blocks in an arrangement that will allow the cistern to sit atop them.

Check again to make sure your cinder blocks are level and adjust the paver base if necessary.

Cisterns

Photo Credit: ECWA

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Once everything's good and level, place the cistern on top of the cinder blocks with the available hose fittings pointing in the direction that you'll use them them most.

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Now that your cistern is in place, make sure that is it level.

If the cistern is leaning one direction even a small amount, you will see a decrease in water storage.

Cisterns

Photo Credit: ECWA

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Cut your downspout just above the level of the cistern and install an elbow downspout fitting in the direction of the cistern.

Add additional lengths of downspout until it rests just over the top of the cistern.

Cisterns

Photo Credit: ECWA

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Finally, make sure your downspout has a place to overflow.

Attach lengths of PVC pipe and any necessary turn fittings until your overflow points away from the cistern and the building.

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Once that looks good, use PVC primer and glue to create a water-tight overflow.

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There you have it!

Your cistern is ready for use!

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Photo Credit: ECWA

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Questions? Comments?
Share a photo of your project?

Cisterns

Photo Credit: ECWA

ECWA has created a maintenance guide to help you get the most out of this Creek SmartĀ® addition to your property.

View or download the


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