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Example Stormwater Harvesting and Use System Schematic

Harvest and reuse is the practice of collecting and/or storing stormwater on site to be used in water applications as needed. Harvest and reuse systems use collected water from various sources, treats them, and then reuses this water on site for different purposes such as irrigation or water features. This practice mitigates the users cost for water, reduces the site's stormwater runoff, and prevents pollution runoff.

Sites containing these systems are not regulated by the EPA but may be regulated by the state through the Safe Drinking Water Act or the Clean Water Act. Water harvest and reuse systems are regulated in Minnesota by Minnesota Rules Section 4714, chapter 17.

Rainwater harvesting is categorized into two types of harvest:

• Surface runoff harvesting
• Rooftop harvesting

Both categories of rainwater harvesting follow the same principles for stormwater reuse. When the rainwater falls onto the site the water is collected through a series of conveyance systems into a storage system, the water is then treated and stored, and the user applies it to their site through a distribution system for the designed purpose. Some designed purposes can be:

• Irrigation systems
• Potable water resources (with treatment)
• Urinal flushing
• Water features
• Vehicle, building, and street cleaning
• Fire suppression systems

Harvest and reuse systems are excellent stormwater treatment practices due to the pollutant removal mechanisms they can be paired with such as vegetative filtering, settling, evaporation, infiltration, transpiration, biological and microbiological uptake, and soil adsorption. Additionally, the pollutants stay on site instead of being flushed downstream. These systems are particularly effective when used for irrigation on C and D soils where traditional infiltration practices are less effective.

Green infrastructure and multiple benefits

Benefit	Effectiveness	Notes
Water quality	◕	Primary benefit is retention of sediment and associated pollutants; nutrient cycling in properly functioning wetlands; may export phosphorus if not designed and maintained properly.
Water quantity/supply	◕	Rate control, flooding benefit.
Energy savings	◑
Climate resiliency	◔	Provides some rate control. Impacts on carbon sequestration are uncertain.
Air quality	◔
Habitat improvement	◔	Use of perennial vegetation and certain media mixes promote invertebrate communities.
Community livability	◑	Aesthetically pleasing and can be incorporated into a wide range of land use settings.
Health benefits	◔
Economic savings	◑	Generally provide cost savings vs. conventional practices over the life of the practice.
Macroscale benefits	◔	Individual practices are typically microscale, but multiple practices, when incorporated into a landscape design, provide macroscale benefits such as wildlife corridors.
Level of benefit: ◯ - none; ◔ - small; ◑ - moderate; ◕ - large; ● - very high

Green infrastructure (GI) encompasses a wide array of practices, including stormwater management. Green stormwater infrastructure (GSI) encompasses a variety of practices primarily designed for managing stormwater runoff but that provide additional benefits such as habitat or aesthetic value.

There is no universal definition of GI or GSI (link here for more information). Consequently, the terms are often interchanged, leading to confusion and misinterpretation. GSI practices are designed to function as stormwater practices first (e.g. flood control, treatment of runoff, volume control), but they can provide additional benefits. Though designed for stormwater function, GSI practices, where appropriate, should be designed to deliver multiple benefits (often termed "multiple stacked benefits". For more information on green infrastructure, ecosystem services, and sustainability, link to Multiple benefits of green infrastructure and role of green infrastructure in sustainability and ecosystem services.

Green Infrastructure benefits of harvest and reuse systems

• Water quality: Installation of harvest and reuse systems prevents or reduces a sites’ total pollution runoff amount
  • Reduces downstream water treatment levels when water is stored on site
  • Wastewater treatment requirements may be reduced due to the incorporation of reuse systems that use on site water for functions such as urinal flushing, water features, and sprinkler systems
• Water quantity and hydrology:
  • Reduction in total water volume movement on the site through water retention techniques and retardation of peak flow from rainfall events at the site
  • Harvest and reuse systems designed with storage containers are better able to withstand drought conditions than sites without them (Costs, Benefits, or Function? What Really Drives Water Reuse)
• Energy:
  • Harvest and reuse systems provide indirect energy savings through reduced water treatment and distribution required by outside sources
  • Harvest and reuse systems used to irrigate vegetation that provide shade, trees and plants, reduce air conditioning and heating costs (Using Trees and Vegetation to Reduce Heat Islands | US EPA)
• Air quality:
  • Air quality impact is minimal, most benefits are indirect through vegetation grown by the harvest and reuse system
• Climate resiliency
  • Site water containment in harvest and reuse systems offers some reduction in flooding during rainfall events
  • Plant vegetation grown with reuse irrigation systems provide carbon sequestration
  • Reduction in pollutant runoff and wastewater treatment lowers total energy consumption and lowers the amount of chemicals needed to produce useable water for the site; this reduction in energy also lowers greenhouse gas requirements
  • Reduction of the heat island effect when reuse systems are used to support a healthy on-site vegetation that provides shade (What You Can Do to Reduce Heat Islands | US EPA)
  • Lower greenhouse gas emissions through reduced air conditioner use (Report Finds Onsite Water Reuse Can Boost Affordable Housing, Spread Climate Resilience – Texas Living Waters Project)
  • The promotion of vegetation and biota growth, vegetative filtering, soil adsorption, and gravitational settling of pollutants that would otherwise be moved by rainfall events and create toxic blooms such as the algae blooms in the Gulf of Mexico
• Habitat improvement
  • Reduction of soil erosion from water runoff and increased soil stability promotes vegetation growth
  • Less of a temperature impact to streams and rivers that receive water discharge and serve as fish and wildlife habitats
• Community livability
  • Harvest and reuse systems help to protect recreation sites for people by ensuring safe and healthy access to water sources and promotes on-site watering availability
  • Water harvest and reuse are adaptable to meet needs such as community gardening, water fountain structures, promoting healthy green spaces, and may be used for recreation purposes if water quality requirements are met
  • Water harvesting and reuse that promotes healthy landscaping can promote mental health improvements for those who frequent them (What are the physical and mental benefits of gardening? - MSU Extension)
  • Larger reuse systems involved with irrigation practices involving trees and other shade proving vegetation reduce temperature levels (Reducing Urban Heat Islands: Compendium of Strategies: Trees and Vegetation (epa.gov))
• Health benefits:
  • Reduction of downstream buildup of nutrients, pathogens, metals, TSS, and phosphorus among others as an indirect, off site benefit
  • Increased longevity for fish and wildlife in the area through the reduction of compounds that wash into waterways as rain runoff
  • Mental health improvements for the people who visit and live in areas that use reuse systems when reuse systems are used in conjunction with landscaping practices (What are the physical and mental benefits of gardening? - MSU Extension)
• Economic benefits and savings:
  • Harvest and reuse systems can be expensive to install but they can reduce the total operating water cost for a building, site, or water features once they are implemented
  • Well maintained harvest and reuse systems combined with vegetation can improve property aesthetics that increase property value
  • Harvest and reuse systems provide a safeguard against drought conditions through stored water that can be used to keep landscaping alive and well over several days or weeks if necessary
  • Potential for more affordable housing conditions when implemented as part of a renting strategy (Report Finds Onsite Water Reuse Can Boost Affordable Housing, Spread Climate Resilience – Texas Living Waters Project)

Design considerations

Maximizing specific green infrastructure (GI) benefits of constructed areas requires design considerations prior to installation. While site limitations cannot always be overcome, the following recommendations are given to maximize the GI benefit of water harvesting and reuse.

Note: Harvest and reuse systems are a good stormwater treatment practice when used in a treatment train. Under the Minnesota Construction Stormwater Permit GI, if Class D soils are present on the site infiltration practices cannot be used. Class A soils are the most desirable for infiltration but infiltration can also be successful with B or C soils. These notes are not mandates nor are they a complete list of what is the best practice for each site, site consideration needs will be addressed by the building design team.

--- Maybe add a chart indicating soil penetrability of different HSG groups —

Caution: The following discussion focuses on design considerations. All benefits delivered by the practice require appropriate construction, operation, and maintenance of the practice. O&M considerations should be included during the design phase of a project. For information on O&M for GSI practices, see Operation and maintenance of green stormwater infrastructure best management practices

• Water quality
  • The designer should consider the project site pollutant sources during design and determine if additional stormwater treatment measures are required for use, what level of pretreatment is needed, and whether first flush diverters are appropriate. For more information on pollutant sources and pretreatment needs see Water quality considerations for stormwater and rainwater harvest and use/reuse. Also see information on Pretreatment.
  • The designer should consider first flush diverters in the collection system design to bypass high pollution loads during snowmelt or pollutant laden events when necessary to meet the requirements of the water use. However, first flush diverters should be utilized with caution ([1]; [2]).
  • Designer should place the appropriate settlement and solid removal procedures in the treatment train to prevent their entry into the reuse containment system
  • Design the site container to maximize capture and storage of runoff and prevent short-circuiting during rainfall events. See Determining the appropriate storage size for a stormwater and rainwater harvest and use/reuse system and Estimating the water balance for a stormwater and rainwater harvest and use/reuse site.
• Water quantity and hydrology:
  • Size the system to meet the intended uses of the harvest system. This includes ensuring appropriate water supply in response to demand. See Determining the appropriate storage size for a stormwater and rainwater harvest and use/reuse system and Design criteria for stormwater and rainwater harvest and use/reuse.
  • Construct the distribution system to reach all areas of the site that require water when economically feasible
  • Determine the sites’ water needs for vegetation and plant systems over a given time period and design the water storage container to meet these needs. Typically, harvest systems are designed and built with a specific use and vegetation scheme in mind, but if feasible, consider adopting vegetation to an intended harvest system (i.e. if the objective is driven by performance goals for the harvest system, vegetation considerations should be built into the design considerations).
  • Utilize tandem systems which combine multiple storage units, such as multiple rain barrels in sequence (Kwiatkowski, 2012)
  • Determine the feasibility of distributed systems, which employs a combination of residential (parcel) harvesting, neighborhood harvesting, and regional harvesting, matching the system to the appropriate storage capacity (Nguyen et al., 2022).
• Climate resiliency:
  • Incorporate vegetation into the water reuse system to help remove pollutants and reduce the sites’ carbon footprint
  • Establish water reuse systems that will meet the vegetation needs for the site and provide adequate water for growth and maintenance
  • Construct the water reuse system in the area best for interception of pollutants
• Habitat improvement:
  • When using water reuse systems that will have direct interactions with people, ensure the appropriate treatment techniques are used to meet the necessary water standards
  • Rainwater harvest systems can be designed to benefit wildlife. Though many of these designs are for livestock applications, some can be modified for use on individual parcels in urban and semi-urban areas (Texas Cooperative Extension, 2014. Designer should be aware of the wildlife of the area and ensure any treatment measures, especially ones that use chemicals, do not pose a threat to the wildlife and their ecosystem.
  • Water reuse systems can establish vegetation that can attract pollinators and promote plant propagation
  • Develop conveyance systems in such a way to minimize changes in temperature that can be detrimental to cold water fish habitats. Give particular consideration to runoff from roofs. be aware that water from constructed ponds and wetlands may have elevated temperatures.
• Community livability:
  • Include recreational infrastructure and interpretative signs
  • Ensure safety of water harvest and reuse systems and adjacent areas by making the storage container inaccessible to unauthorized individuals
  • Conduct surveys prior to and after development to identify features that enhance education, recreation, and other benefits of water reuse systems that are desirable to the served customer/community/stakeholder
  • Design grown vegetation and plantings with easy access (e.g. locate close to road, create public access)
  • Create attractive slopes using vegetation and proper erosion protection
• Health benefits:
  • Design storage containment systems for safety. Minimize the depth needed for pooled water if the containing area is exposed. Minimize access to infiltration or other treatment train areas by planting shrubs, fencing, or other area denial systems. Additionally, properly mark the area with signs. Minimizing depth of infiltration systems reduces hazards for children.
  • Infiltration systems naturally control mosquito habitats by going dray within a few days compared to typical stormwater ponds
• Economic benefits and savings:
  • Maximize sight-lines to the vegetation that the water reuse system services
  • Integrating water reuse into landscape design, including creating habitat, pathways, picnic areas, etc can increase property value

The Pollution Control Agency allows for infiltration to be used as a credit source when meeting pollutant budgets for Total Suspended Solids (TSS) and Total Phosphorus (TP). The methodology for counting credits can be found here.

Additional Information: Water harvest and reuse systems are effective for use in class C and D soils Harvest and reuse systems can be incorporated in a useful and beneficial manner to site owners. An example of a well designed harvest and reuse system that serves multiple purposes can be found in Thailand at the Chulalongkorn University

Recommended reading

• [https://pacinst.org/wp-content/uploads/2020/06/Scaling-Green-Stormwater-Infrastructure-Through-Multiple-Benefits-in-Austin-Texas_Pacific-Institute_June-2020.pdf Scaling Green Stormwater Infrastructure

Through Multiple Benefits in Austin, Texas: Distributed Rainwater Capture on Residential Properties in the Waller Creek Watershed] - Sarah Diringer, Morgan Shimabuku, Heather Cooley, Madeline Gorchels, Jennifer Walker, and Sharlene Leurig; 2020.

• Water Reuse and Recycling - US EPA
• Basic Information about Water Reuse - US EPA
• Stormwater Harvesting and Reuse Study - Minnehaha Creek Watershed District
• Reducing and Reusing Basics - US EPA