Rainwater Harvesting Information
Disclaimer
This website does not necessarily represent the views of the City of San Diego or its employees. The City of San Diego assumes no legal liability for the accuracy, completeness, or usefulness of information in this report. The contents of this website are provided for general education and informational purposes only. The City of San Diego highly recommends that the reader consult with a technical professional and/or product retailer before applying any of this information to a specific project.
Rainwater harvesting is a technique used for collecting, storing, and using rainwater for landscape irrigation and other uses. The rainwater is collected from various hard surfaces such as roof tops and/or other types of manmade above ground hard surfaces. This ancient practice is currently growing in popularity throughout our communities due to interest in reducing the consumption of potable water and the inherent qualities of rainwater. This web site will mainly focus on general information about rainwater harvesting systems, rain water system advantages and disadvantages, and helpful links and references.
Rainwater systems come in all shapes and sizes, from simple catchment system under a downspout to large above and/or underground cisterns with complex filtration systems that can store thousands of gallons of water. Most rainwater collection systems are comprised of the following basic components:
- Catchment surface – rooftop or other raised solid surface. The best catchment systems have hard, smooth surfaces such as metal roofs or concrete areas. The amount of water harvested depends on the quantity of rainfall, and the size of the surface and the slope of the catchment area.
- Gutters and downspouts – also known as distribution systems that channel the water from the catchment area to a holding container such as a barrel, cistern, planted area, etc.
- Leaf screens – a screen that removes or catches debris.
- Roof washers – a device that diverts the “first flush” of rain before it enters the storage tank. Most rainwater suppliers recommend that the “first flush” of water is diverted to an outside area of the storage system, since the catchment surface may accumulate bird droppings, debris and other pollution.
- Storage tanks – In general, the storage tank is the most expensive component of a rainwater harvesting system. There are numerous types and styles of storage tanks available. Storage can be above-ground or underground. Storage containers can be made from galvanized steel, wood, concrete, clay, plastic, fiberglass, polyethylene, masonry, etc. Examples of above-ground storage include; cisterns, barrels, tanks, garbage cans, above ground swimming pools, etc. Storage tank prices vary based on different variables such as size, material and complexity. To inhibit the growth of algae, storage tanks should be opaque and preferably placed away from direct sunlight. The tanks should also be placed close to the areas of use and supply line to reduce the distance over which the water is delivered. Also consider placing the storage at an elevated area to take advantage of gravity flow. The tank should always be placed on a stable and level area to prevent it from leaning and possibly collapsing.
- Delivery systems – gravity-fed or pumped to the landscape or other end use areas.
- Purification/treatment system - needed for potable systems to make the water safe for human consumption. Please check with your local health department for information on filtration systems and certification requirements. Information is available at the County of San Diego Department of Environmental Health - Small Drinking Water Systems. Additional information available at California Department of Public Health.
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Rain gutters and downspout with debris filter
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Storage tank shown with an inlet pipe and overflow tube
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Inlet pipe with debris filter
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Rain barrel at San Ysidro Library
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Serial connected rain barrels
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Rain barrel overflow tube
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Rainwater Harvesting Advantages
- Makes use of a natural resource and reduces flooding, storm water runoff, erosion, and contamination of surface water with pesticides, sediment, metals, and fertilizers
- Reduces the need for imported water (the San Diego region imports between 80%-90% of its water from Northern California and Colorado River)
- Excellent source of water for landscape irrigation, with no chemicals such as fluoride and chlorine, and no dissolved salts and minerals from the soil
- Home systems can be relatively simple to install and operate May reduce your water bill
- Promotes both water and energy conservation
- No filtration system required for landscape irrigation
Rainwater Harvesting Disadvantages
- Limited and uncertain local rainfall
- Can be costly to install – rainwater storage and delivery systems can cost between $200 to $2,000+ depending on the size and sophistication of the system
- The payback period varies depending on the size of storage and complexity of the system
- Can take considerable amount of time to “pay for itself”
- Requires some technical skills to install and provide regular maintenance
- If not installed correctly, may attract mosquitoes (i.e.; West Nile Disease and other waterborne illnesses)
- Certain roof types may seep chemicals, pesticides, and other pollutants into the water that can harm the plants
- Rainwater collected during the first rain season is generally not needed by plants until the dry season. Once catchment is full, cannot take advantage of future rains
Parents/adults:
Please make sure that children and pets do not climb on the storage systems and accidentally fall into the storage tank.
Storage tanks should have locking lids and/or bars that keep the children and pets out!
Rainwater harvesting policies vary from state to state. However there are no known local laws restricting rainwater harvesting at this time. In 2007, two bills were passed in the California State Legislature that requires local water districts to create water conservation programs and building standards: AB1420 and AB 1560; however neither bill discusses rainwater harvesting as a water conservation option. The American Rainwater Catchment Systems Association (ARCSA) has developed a standards guide that is being proposed to the International Association of Plumbing and Mechanical Officials (IAPMO) inclusion in the Sustainable Plumbing Standard.
The City of San Diego’s Storm Water Pollution Prevention Program is currently conducting a pilot study on rainwater harvesting at seven locations throughout the city’s watersheds. Information about the pilot project will be available soon on the “Think Blue” web site at www.sandiego.gov/thinkblue.
