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Are Rain Barrels or Cisterns Feasible for My Project? Rain barrels and cisterns are appropriate for sites with the following characteristics: Roof areas that drain to downspouts. A level, firm surface is needed to support a rain barrel(s) or cistern to prevent shifting or falling over. A full 55-gallon rain barrel will weigh over 400 lbs. A landscaped area where the captured water can be used (and where it can be drained by gravity flow) should be located within a reasonable distance from the rain barrel(s). A landscaped area or safe path to the storm drain system that can handle overflow. How Much Storage is Recommended? The number of rain barrels recommended to capture runoff from a given roof (or other impervious area) is shown in the following table. Roof or Impervious Area (sq. ft.) Suggested Minimum Number of 55 Gallon Rain Barrels* Up to 750 1-2 750 – 1,250 2-3 1,250 – 1,750 3-4 1,750 – 2,250** 4-5 * Or equivalent capture using larger rain barrels or a cistern. To harvest rainwater from an area greater than 2,250 sq. ft. install 1 additional rain barrel per each additional 500 sq. ft. RAIN BARRELS AND CISTERNS Stormwater Control for Small Projects Bay Area Stormwater Management Agencies Association Approved August 23, 2012 Rain barrels and cisterns can be installed to capture stormwater runoff from rooftops and store it for later use. They are low-cost systems that will allow you to supplement your water supply with a sustainable source and help preserve local watersheds by detaining rainfall. Collected rainwater may be used for landscape irrigation. Subject to permitting requirements, harvested rainwater may be allowed for toilet flushing; contact municipal staff for more information. Capturing even a small amount of your roof runoff will have environmental benefits because it will reduce the quantity and speed of stormwater runoff flowing to local creeks. Rain barrels typically store between 50 and 200 gallons. They require very little space and can be connected or “daisy chained” to increase total storage capacity. Cisterns are larger storage containers that can store 200 to over 10,000 gallons. These come in many shapes, sizes, and materials, and can be installed underground to save space. Daisy chained system of 205-gallon rain barrels Courtesy of The City of Oakland Page 1 ---PAGE BREAK--- Pervious Cement Components of a Rainwater Harvesting System Gutters and Downspouts Properly sized and maintained gutters and downspouts are essential to a rainwater harvesting system. Strategically locate any new downspouts in an area where the rain barrel or cistern will be most useful. Consider the height of the rain barrel and the first flush device. Existing downspouts may have to be shortened to make room for the rain barrel and first flush device. Install a fine mesh gutter guard on gutters to keep leaves and other debris from entering and clogging the gutters. This will reduce the need for cleaning gutters and the rain barrel or cistern. As needed, consult a professional roofer to aid in gutter and downspout installation. Roofing Materials Technically, any impervious surface can be used for harvesting rainwater; however, the surface materials will affect the quality of captured rainwater, which has implications for the recommended uses. Although it is technically possible to harvest runoff from parking lots, patios, and walkways, it is more difficult since a subterranean cistern or a pump is usually needed to move the water into an above-ground rain barrel or cistern. Also, there are typically greater levels of debris and contaminants that must be filtered out of the runoff before it enters the storage system. Due to these complexities, it is more common to harvest rainwater from rooftops, which is the focus of this fact sheet. When designing your system, consider the roofing material on the building. If you have asphalt or wooden shingles, use the harvested rainwater only for non-edible landscapes, unless the water is treated first. Petroleum or other chemicals from these roofing materials can leach into the rain water. Roofs with cement, clay, or metal surfaces are ideal for harvesting water for a wide variety of uses. Wood shingle roof Courtesy of Gutter Glove This gutter is covered by a fine mesh gutter guard to keep debris out. Courtesy of Gutter Glove Page 2 ---PAGE BREAK--- Components of a Rainwater Harvesting System Foundation and Overflow Before installing a rain barrel or cistern, prepare the site so that the system will function safely. Find or create a level location near the downspout on which to place the rain barrel or cistern. A concrete or stone paver foundation may be appropriate for smaller rain barrels. A more substantial foundation will likely be required for large cisterns. Secure rain barrels and cisterns to your structure with metal strapping, or anchor to the foundation, to prevent tipping in an earthquake. Maintain clear access to the rain barrel outlets and cleaning access points. Design an overflow path, so that overflow from the rain barrel(s) will discharge safely to a landscaped area, or storm drain system. Where possible, direct overflow to a rain garden, swale, or other landscaped area to maximize retention of rainwater onsite. Direct the overflow away from the rain barrel, building foundation, and neighboring properties. Consult with the municipality to identify overflow locations. Rain Barrel and Cistern Accessories to Keep Water Clean Various accessories to rain barrels and cisterns help protect the quality of harvested water and reduce maintenance. These accessories include “first flush” diverters, filters, and screens. Leaves, twigs, sediment, and animal waste are common in runoff, especially at the beginning of a storm (“first flush”). This debris can result in clogging and encourage bacterial growth. A first flush diverter helps remove debris and contaminants by directing the first few gallons of runoff from the roof to landscaping, away from the rain barrel or cistern. The following tips will help you keep the water in your system clean. Install a first flush diverter directly under your downspout. You may have to cut the downspout to connect the first flush diverter above the rain barrel. Use the same diameter pipe for the first flush diverter, the downspout, and the connector to the rain barrel. Avoid changing diameters of pipes in order to keep the system from backing up. Design the first flush diverter to discharge the first flush to non-edible landscaping. Install mosquito-proof screens under the lid of the rain barrel and inside the overflow outlet. First flush and downspout diverter installation Courtesy of The City of Oakland Large unit installed at a single family residence. Courtesy of Stephanie Morris Page 3 ---PAGE BREAK--- Operation and Maintenance After installing your rain barrel or cistern, follow these tips for long-term safety and functionality. Regularly check the gutters and gutter guards to make sure debris is not entering the rainwater harvesting system. Inspect the screens on the rain barrel or cistern prior to the wet season to make sure debris is not collecting on the surface and that there are not holes allowing mosquitoes to enter the rain barrel. Inspect screens more frequently if there are trees that drop debris on the roof. Clean the inside of the rain barrel once a year (preferably at the end of the dry season when the rain barrel has been fully drained) to prevent buildup of debris. If debris cannot be removed by rinsing, use vinegar or another non- toxic cleaner. Use a large scrub brush on a long stick, and avoid actually entering the rain barrel. Drain washwater to landscaping. Clean out debris from cisterns once a year, preferably at the end of the dry season. When installing rain barrels and cisterns, consider the following criteria unless otherwise instructed by the municipality. Do not use flexible piping, to prevent mosquito breeding in water that may pool in flexible pipes. If irrigating edible landscapes, consider pipes that meet FDA food grade standards. When designing the overflow path, remember that in heavy storms rain barrels and cisterns will overflow. A 1,000-sq.-ft. roof will produce about 600 gallons of runoff during a storm that has produces a depth of 1 inch of rain. There shall be no direct connection of any rain barrel or cistern and/or rainwater collection piping to any potable water pipe system. Rainwater systems shall be completely separate from potable water piping systems. Place the bottom of the barrel at a higher elevation than the landscape, to use gravity flow. All rain barrels and cisterns should have a screen to ensure mosquitoes cannot enter. Allow overflow to drain to your landscape or a rain garden. Ensure that areas receiving overflow do not have standing water for more than 48-hours. The low water pressure from a small rain barrel will not operate in-ground sprinkler or low- volume devices. Consider using a soaker hose. If using a soaker hose, remove the pressure- reducing washer to increase the water flow. If the water is not needed for irrigation during the rainy season, consider releasing the water to a vegetated area between storms, so the barrels will be empty to catch rain from the next storm. This will help protect your watershed by reducing the quantity and speed of water entering local creeks during storms. Install a spigot and drip tape to allow the rain barrel or cistern to slowly drain between storms. You can store the water captured towards the end of the rainy season to irrigate your garden in the dry season. For more information, ask municipal staff to refer you to countywide stormwater guidance. Design Checklist Daisy-chained system Courtesy of Acterra The City of Los Angeles and Geosyntec Consultants are acknowledged for providing text and formatting used in this fact sheet. The City of Oakland, Acterra, Gutter Glove, and Stephanie Morris are acknowledged for images used in the fact sheet. Page 4