Cost-benefit considerations for stormwater and rainwater harvest and use/reuse Cost-benefit considerations for stormwater and rainwater harvest and use/reuse

What are the total costs and cost per element of a harvesting and use system? Costs can be highly dependent on the situation and context. The total cost of a harvest and use system can be divided into the four major components of a harvesting and use system:

• Collection
• Storage
• Treatment
• Distribution

The individual components required to construct each of the four systems usually depends on the site and/or use of the water. For the collection component, storm sewer pipes and roof drains may already be part of the design, thus reducing cost. The storage component is typically the largest cost item. If storage already exists at a site, such as existing wet ponds, providing storage for a harvest and use system can be done at minimal cost. Treatment costs can vary dramatically, depending on the source water and the end use, from virtually no treatment to meeting drinking water standards. Costs for distribution are usually associated with connection to an irrigation system. The location and elevation of the irrigation site in proximity to the source and storage areas affect the amount of pipes and pumps needed. If a site already has an irrigation system in place drawing from a potable water source, the distribution portion of the system costs may be minimal.

The site setting affects the cost of harvest and use systems. For example, in highly urban areas the choices for stormwater treatment may be limited and components such as storage (which is often an underground cistern) may be quite expensive on a cost/unit treatment basis. However, harvest and use may still more cost-effective than other stormwater management techniques such as green roofs or underground infiltration facilities. It is difficult to compare unit costs of harvest and use systems across different settings.

Total system costs

The total cost of a stormwater harvest and use system varies due to the large range in the size and scale of these systems. In a Minnesota Pollution Control Agency (MPCA, 2016) survey for stormwater harvest and use systems in the Twin Cities Metropolitan Area, 26 respondents provided total system cost information, summarized in the MPCA survey responses of total stormwater harvest and use system costs graph below. Total costs ranged from 💲1,500 to 💲1,500,000, with eight systems over 💲400,000. Of the 26 systems with cost information, 22 were irrigation systems (💲1,500 - 💲1.5M), 1 was a toilet flushing system (💲300,000), 1 was a toilet flushing and vehicle washing system (💲57,500), and 2 were irrigation and vehicle washing systems (💲10,000 - 💲425,000).

MPCA survey responses of total stormwater harvest and use system costs

Individual component costs

Major individual component costs of stormwater harvest and use systems include land acquisition, excavation and material removal, and the storage/treatment systems. Very little detailed component cost information is currently available because costs for many of the storage and treatment systems are packaged together. Examples of harvest and use system itemized costs are discussed below.

The 2011 Met Council Stormwater Reuse Guide developed a list of stormwater harvest and use system construction activity components and cost units for developing system cost estimates, reproduced in the Stormwater Harvesting and Use Component Checklist and Cost Units table. A cost analysis of different cistern materials was summarized by CONTECH Inc. in their 2011 Cistern Design Considerations for Large Rainwater Harvesting Systems Professional Development Advertising article, reproduced in the Comparison of materials used for rainwater harvesting systems table below. Some itemized component cost information was also compiled in the Texas Manual on Rainwater Harvesting, summarized in the Itemized stormwater harvest and use system component costs table below. These itemized costs include cistern and gutter costs on a per volume/length basis, and treatment system consumables (such as filters and cartridges) that must be replaced regularly as part of normal system operation and maintenance.

Comparison of materials used for rainwater harvesting systems

Link to this table

	Material	Cost low - high	Installation hard - easy	Longevity short - long	Durability low - high	Maintenance Access hard - easy	Best Use Capacity (gallons)
Underground	FiberglassX	💲💲💲💲💲	●●●○○	●●●●○	●●○○○	●●●●○	5,000 to 30,000
	Polyethylene	💲	●●●●●	●●●○○	●●●○○	●●○○○	> 5,000
	Steel Reinforced Polyethylene (SRFE)	💲💲💲	●●●●○	●●●●●	●●●●●	●●●●○	10,000 to 100,000+
	Plastic Crates	💲💲💲	●●●○○	●●○○○	●○○○○	●○○○○	5,000 to 50,000
	Concrete	💲💲💲💲💲	●●○○○	●●●●○	●●○○○	●●●●○	30,000+ (with high loading)
	Fabricated Steel	💲💲💲💲	●●●●○	●●●○○	●●●●○	●●●●○	not recommended
	Waterproof Corrugated Metal	💲💲	●●●●○	●●●○○	●●●●●	●●●●○	5,000 to 30,000
Above-Ground	Monolithic	💲💲💲	●●●●○	●●●●●	●●●●○	●●●●●	Up to 20,000
	Plate Assembled On-Site	💲💲💲	●●○○○	●●●●●	●●●●○	●●●●●	15,000+

Itemized stormwater harvest and use system component costs
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System	System Component	Cost	Cost Recurrence
Materials	Tanks	💲0.50/gallon for fiberglass to 💲4/gallon for wielded steel tank
	Gutters	💲0.30/foot for vinyl/plastic to 💲6 - 12/foot for aluminum/galvalume
Annual maintenance (costs will be dependent on system size)	Cartridge Filter	💲20-60	Filter must be changed regularly
	Reverse Osmosis Filter	💲400-1,500	Change filter when clogged (depends on turbidity)
	UV Light Disinfection	💲350-1,000; 💲80 to replace UV bulb	Change UV bulb every 10,000 hours or 14 months
	Ozone Disinfection	💲700-2,600; 💲1,200+ for in-line monitor to test effectiveness
	Chlorine Disinfection	💲1/month manual dose or a 💲600-3,000 automatic self-dosing system

Stormwater Harvesting and Use Component Checklist and Cost Units

Link to this table

Phase	Component	Unit	Check if required for system:
Collection	Cleaning of roof (if retrofit project)	Square foot
	Roof washing system	Each
	Gutters	Linear foot
	Gutter screens	Linear foot
	Downspouts	Linear foot
	Scuppers	Each
	Catch basins	Each
	Catch basin filters	Each
	Manholes	Each
	Oil/water separators	Each
	Storm sewers	Linear foot
	Bypass valves	Each
	First flush diverter	Each
Storage – Ponds/ basins	Site demolition	Varies
	Excavation	Cubic foot
	Disposal of excess soil	Cubic foot
	Vegetation restoration	Square foot
	Baffles at outlet	Linear foot
	Filters at outlet	Each
	Outlet structure	Each
	Pumping system including pump, motor, valves, and pressure tank (for non-gravity and pressurized systems)	Varies
	Aeration	Varies
	Electrical supply (for pumps or aeration)	Varies
Below-ground storage	Site demolition	Varies
	Excavation and backfill	Cubic foot
	Imported aggregate bedding material	Cubic foot
	Disposal of excess soil	Cubic foot
	Vegetation or pavement restoration	Square foot
	Pre-fabricated tanks	Each
	Baffles, calming inlet, and/or filters, if not supplied with pre-fabricated tank	Each
	Cast-in-place concrete tank	Varies
	Pumping system including pump, motor, valves, and pressure tank (for non-gravity and pressurized systems)	Varies
	Maintenance access manhole	Each
	Electrical supply (for pumps)	Varies
Treatment systems	Piping	Linear foot
	Valves	Each
	Flow meter (when needed to regulate chemical feed)	Each
	Electrical supply	Varies
	Maintenance access manhole (if located underground)	Each
	Backflow prevention valves (if connected to potable water for supplemental supply and/or for filter backwash)	Each
	Suspended & Colloidal Solids Removal Systems Chemical feed Tank with baffles or mixing device (if chemicals not fed into inline mixing device) Settling basin with dewatering valves for solids removal	Varies
	Residual Suspended Solids Removal Systems Filter chamber containing activated carbon or other filter media, including piping and valves for bypass and backwash (for filtration systems) Tank with micro-bubble diffusion, dewatering valves, and surface skimmer (for dissolved air flotation systems)	Varies
	Residual Colloidal Solids Removal Systems Filter chamber containing multi-media, including piping and valves for bypass and backwash (for ultrafiltration systems)	Varies
	Dissolved Solids Removal Systems pH feed (for reverse osmosis systems) Chemical feed (for electrodialysis systems) Filter chamber containing semi-permeable membrane, including piping and valves for bypass and backwash (for all systems) Solids disposal system	Varies
	Disinfection Chemical feed (for continuous chlorine disinfection) Tank with baffles or mixing device (for batch disinfection with chlorine) Contact tank with UV lights and piping (for ultraviolet disinfection) Tank with piping, valves, ozone diffuser (for ozone disinfection) Off-gas ozone destructor tank (for ozone disinfection)	Varies
Distribution	Pumping system including pump, motor, valves and pressure tank	Varies
	Piping for distribution	Linear foot
	Valves for pressure control, and regulating flow	Each
	Valve boxes	Each
	Sprinkler nozzles – impulse, spray, rotating, bubbler, or drip	Each
	Irrigation controllers with wiring to each sprinkler (for automated control systems)	Varies
	Drain plug (for winterization)	Each

Harvest and use system construction bid estimate examples

Due to the large variability in harvest and use system costs, construction bid estimates are provided as examples of itemized costs.

• Installation of 3 – 29,000 gallon underground storage tanks: The Contractor bid averages for installation of three 29,000 gallon underground storage tanks table below summarizes the average of four contractor bids for the installation of three 29,000 gallon underground storage tanks (120” diameter x 50’ length) for an irrigation harvest and use system designed for an approximate 8 acre drainage area and an approximate 3 acre irrigation area. This estimate is for storage (3 tanks) components only. The average capital cost for one gallon of storage is 💲1.46 per gallon. The underground storage tank components were 71 percent of the total installation bid.
• Installation of 1 – 1,500 gallon aboveground tank harvest and use system: The table below summarizes the engineers estimate for installation of one 1,500 gallon aboveground corrugated steel storage tank that captures rainwater from a 2,100 square foot roof connected to a hose for on-site exterior water use. This estimate is for collection (gutters), storage (tank), and distribution (hose) components. The total capital cost for one gallon of storage is approximately 💲20 per gallon. The aboveground storage tank components were 46 percent of the total construction estimate.

Contractor bid averages for installation of three 29,000 gallon underground storage tanks

Link to this table

BASE BID ITEM	ESTIMATED QUANTITY	UNIT	UNIT PRICE AVERAGE	TOTAL AVERAGE BID
Part 1 - General and Erosion Control
MOBILIZATION	1	LS	💲23,340	💲23,340
SEDIMENT CONTROL LOG -- INSTALL, MAINTENANCE AND REMOVAL	267	LF	💲5	💲1,335
TEMPORARY FENCE -- INSTALL AND REMOVAL	160	LF	💲8	💲1,280
STABILIZED CONSTRUCTION EXIT -- INSTALL, MAINTENANCE AND REMOVAL	1	LS	💲2,410	💲2,410
EROSION CONTROL BLANKET	424	SY	$4	$1,696
STORM DRAIN INLET PROTECTION -- INSTALL, MAINTENANCE AND REMOVAL	2	EA	💲387	💲774
DUST CONTROL	10	HRS	💲121	💲1,210
Total Part 1				💲32,045
Part 2 - Removals
REMOVE EXISTING SEDIMENT CONTROL LOG OR SILT FENCE Total Part 2	268	LF	💲4	💲1,072
Total Part 2				💲1,072
Part 3 - Grading
COMMON EXCAVATION -- INCLUDES TANK TRENCH EXCAVATION AND FILL TO PROPOSED GRADE	1955	CY	$9	$9
REMOVAL OF EXCAVATED MATERIAL	1389	CY	$10	$13,890
AGGREGATE BACKFILL	1009	CY	$41	$41,369
Total Part 3				💲72,854
Part 4 – Underground Storage Tank Components
RAINWATER HARVESTING TANK (120" DIA. X 50-FEET)	3	EA	💲77,639	💲232,917
CONSTRUCT DRAINAGE STRUCTURE	6	EA	💲1,153	💲6,918
CONCRETE, REINFORCED COLLAR (RISER MANHOLE CAP)	6	EA	💲1,085	💲6,510
CONCRETE, REINFORCED COLLAR (AT RISER CONNECTION TO TANK)	6	EA	💲1,248	💲7,488
INSTALL CASTING	6	EA	💲1,221	💲7,326
18" HDPE PIPE	115	LF	💲73	💲8,395
SOIL DENSITY COMPACTION TESTING	12	EA	💲430	💲5,160
Total Part 4				💲274,714
Part 5 – Site Restoration
RAPID STABILIZATION	0.42	AC	💲3,173	💲1,333
PERMANENT SEEDING	0.42	AC	💲6,336	💲2,661
TURF ESTABLISHMENT	1	EA	💲2,500	💲2,500
Total Part 5				💲6,494
Total Bid				💲386,590
PRICE PER TANK (3 – 29,000 gallon tanks)				💲129,060
PRICE PER TANK PER YEAR OVER 25 YEAR				💲5,162
PRICE PER GALLON (87,000 gallons)				💲4.44
PRICE PER GALLON PER YEAR OVER 25 YEARS				💲0.06

Engineers estimate for installation of one 1,500 gallon aboveground corrugated steel storage tank

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ITEM	ESTIMATED QUANTITY	UNIT	UNIT PRICE	TOTAL COST
RAINWATER HARVESTING PACKAGE: 1,500 GALLON ABOVE GROUND CORRUGATED STEEL TANK AND ASSOCIATED FITTINGS & ACCESSORIES, INCLUDING PUMP AND FILTER SYSTEM. (72" DIA. X 9')	1	EA	💲15,000	💲15,000
REINFORCED CONCRETE FOUNDATION ON IMPROVED SUBGRADE	1	EA	💲2,500	💲2,500
REMOVE EXISTING GUTTER	60	LF	💲9	💲540
5" BOX GUTTER	222	LF	💲10	💲2,220
GUTTER DOWNSPOUTS	45	LF	💲15	💲675
6" HDPE PIPE	110	LF	💲30	💲3,300
RODENT GUARD	1	EA	💲350	💲350
SCOUR STOP MAT	32	SF	💲30	💲960
EROSION CONTROL BLANKET	14	SY	💲20	💲284
ENGINEER'S REPORT	1	EA	💲2,500	💲2,500
O&M GUIDELINES	1	EA	💲1,500	💲1,500
Total				💲29,829

Funding sources

There are many sources of funding that can be used to finance stormwater harvest and use systems (Stormwater Harvest and Use Funding Sources table). Due to the high cost of these systems, more than one source of funding is often needed. Of the 26 respondents to the 2016 MPCA stormwater harvest and use system survey that provided cost and funding source information, 16 respondents utilized two or more sources of funding to finance their harvest and use system.

Stormwater harvest and use funding sources
Link to this table

Funding Source	Funding Type
Watershed Organization Implementation and Cost-Share Programs	Watershed Management Organization Watershed District Joint Power Agreement
State Agency Grants and Loans	Met Council Stormwater Grant MPCA 319 Fund MPCA Clean Water Partnership Loans Clean Water Land & Legacy Amendment Clean Water Fund Public Facilities Authority Clean Water Revolving Fund
County Funds	County program funds
Municipal Funds and Utility Fees	Enterprise fund Stormwater utility fees Surface water management utility fees
Other Public Financing	University environmental fee School district Student housing fees Parks operating budget
Private Financing	Developers (to meet stormwater requirements on a restricted site or to maximize developable area) Local organizations (e.g. youth soccer club)

Financial incentives and benefits

There are many financial incentives and benefits that should be factored in to the global net cost of a stormwater harvest and use system. These include:

• Points toward U.S. Green Building Council LEED or Institute of Sustainable Infrastructure Envision ratings which demonstrate how well public entities are sustainably managing energy, material, and water resources (LEED) and planning for climate change and long-term resiliency in public infrastructure investments (Envision)
• Reduced potable water utility costs
• Reduced downstream stormwater infrastructure costs
• Increased resiliency in stormwater management and potable water systems due to reductions in stormwater volume and potable water demand
• Ecosystem services

Additional cost resources

Cost-Benefit case studies

• Bill Hicks, P.E. 2008. A Cost-Benefit Analysis of Rainwater Harvesting at Commercial Facilities in Arlington County, Virginia.
• Sarah Lawson, Ph.D. (Rainwater Management Solutions). Sample Rainwater Harvesting Case Study Costco Store in Northern Virginia.

System costs

• Contech Construction Products, Inc. September 2011. Cistern Design Considerations for Large Rainwater Harvesting Systems.
• USEPA. January 2013. Rainwater Harvesting Conservation, Credit, Codes, and Cost Literature Review and Case Studies.

Related pages

• Overview for stormwater and rainwater harvest and use/reuse
• Design criteria for stormwater and rainwater harvest and use/reuse
• Construction specifications for stormwater and rainwater harvest and use/reuse
• Operation and maintenance for stormwater and rainwater harvest and use/reuse
• Water quality considerations for stormwater and rainwater harvest and use/reuse
• Environmental concerns for stormwater and rainwater harvest and use/reuse
• Cost-benefit considerations for stormwater and rainwater harvest and use/reuse
• Case studies for stormwater and rainwater harvest and use/reuse
• Calculating credits for stormwater and rainwater harvest and use/reuse
• Definitions for stormwater and rainwater harvest and use/reuse
• Requirements, recommendations and information for using Harvest and re-use/cistern as a BMP in the MIDS calculator
• Links for stormwater and rainwater harvest and use/reuse
• References for stormwater and rainwater harvest and use/reuse
• Technical support for stormwater and rainwater harvest and use/reuse