The Pacific Northwest National Laboratory (PNNL) in collaboration with the Federal Energy Management Program (FEMP) developed an online GIS-based Rainwater Harvesting Tool to help federal agencies strategically prioritize commercial rainwater harvesting projects by providing rainwater harvesting potential across the United States. The mapping tool provides three layers of data for rainwater harvesting potential:
- State-by-state Rainwater Harvesting Regulations: State-by-state rainwater harvesting regulations.
- Rainwater Harvesting Potential for Year-round Collection: Relative potential to collect rainwater throughout the year across the United States.
- Rainwater Harvesting Potential for Landscape Irrigation: Relative potential to collect rainwater specifically conducive for irrigating landscape.
For more information on the methods used to develop these maps, see the Tool’s Help Guide or read the report by PNNL. The Help Guide also provides information on applying the results of the tool, tips for rainwater harvesting projects and other considerations. A How To Use the Tool Guide explains how to navigate within the tool and how to search for and gather the data.
Rainwater harvesting can provide a key source of alternative water to federal facilities. Rainwater harvesting systems capture, divert, and store precipitation from rooftops for later use. The tool provides a range of available rainwater for harvesting across the U.S. both for general applications and specifically for landscape irrigation.
Most commonly, harvested rainwater is used for non-potable applications such as:
- Landscape irrigation
- Toilet and urinal flushing
- Vehicle wash
- Dust suppression
- Cooling tower makeup
- Ornamental pond and fountain filling.
In addition to providing alternative water, harvesting rainwater can also potentially prevent stormwater from entering waterways, helping agencies meet federal requirements for stormwater management. Reducing stormwater eases flooding and erosion by slowing runoff and allowing it to soak into the ground, turning stormwater problems into water supply assets. Less runoff also means less contamination of surface water from sediment, fertilizers, pesticides, and other pollutants that runoff might transport.
The data used to develop the tool has limitations. Daily precipitation is best for determining how much rainfall is available for harvesting. The tool is based on historical, monthly average rainfall. This does not account for monthly variation such as large rain events, or rainy periods versus dry periods. For example, if there are large rain events at the beginning of the month, there may be minimal rainwater at the end of the month.
Rainwater harvesting may be appropriate for many areas across the U.S. even in areas of low rainfall availability. Important considerations when planning for harvesting projects should include the following:
- Size of catchment area (roof size): A larger roof area can capture significant precipitation even in areas of low rainfall availability
- Rainwater storage capacity: Areas with lower available precipitation may require larger tanks to provide more storage capacity, increased tank size will increase equipment cost
- Water rates: Areas with more expensive water rates should also be considered when prioritizing locations for rainwater harvesting projects
- Operation and maintenance: Rainwater harvesting systems require regular operation and maintenance; when prioritizing sites for projects, make sure to consider available staff that can operate and maintain the system (See FEMP's Best Management Practice #14: Alternative Water Sources)
- Regulations: Some states limit rainwater harvesting, so check the tool’s mapping layer on state regulations to make sure it is allowed.
- Permits: Rainwater harvesting permits may be required; check with local or state government
- Turf replacement (landscape irrigation only): Consider replacing traditional turf with native landscaping that requires significantly less water and can make rainwater harvesting a viable option in many areas of the U.S.