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Nashville receives an average of 48 inches of rain each year. Every drop that hits your roof is free water — for your garden, your livestock, your laundry, your landscape, and with proper treatment, your glass. Standing seam metal roofing offers the highest collection efficiency of any roofing material on earth. This page explains why, how much water your roof can actually harvest, and how to build a system that captures it.
The American Rainwater Catchment Systems Association is the leading professional organization for rainwater harvesting in the United States. Their recommendation of standing seam metal roofing for potable (drinkable) water collection is significant — it is the only conventional roofing material they endorse for this use without requiring an additional coating or membrane.
The key qualifiers in the ARCSA recommendation are the finish and the fastener system. The finish must be non-toxic — powder coated, enameled, or a high-quality baked-on paint system like PVDF (Kynar 500) or SMP (silicone-modified polyester). The fastener system matters because standing seam's concealed clips mean no exposed screws penetrating the collection surface, eliminating the rubber washer degradation and exposed metal-to-metal contact points found on screw-down panels.
*Estimated monthly collection volumes based on 2,000 sq ft roof footprint with 95% collection efficiency. Actual collection varies by storm intensity, duration, system configuration, and first-flush diversion losses.
The constant 0.623 converts inches of rain over a square foot to gallons. Standing seam metal efficiency = 0.95 (95%).
These figures represent theoretical maximum annual collection based on average Nashville precipitation and 95% runoff coefficient. Actual collection is reduced by first-flush diversion, system losses, evaporation during light rains, and storm intensity patterns. Real-world collection is typically 75–90% of theoretical maximum.
That is155 gallons per dayon average — enough to flush every toilet in the house, run every load of laundry, water a substantial garden, and still have reserves.
Assumes 2,000 sq ft roof footprint with standing seam metal at 95% collection efficiency. Actual results vary.
To put 56,800 gallons in perspective: the average American household uses approximately 80–100 gallons of water per person per day. A family of four uses roughly 300–400 gallons daily, or 110,000–146,000 gallons per year. A standing seam roof on an average Nashville home can theoretically harvest 40–50% of a family's total water consumption — and with modest conservation, that percentage climbs significantly.
For non-potable uses like garden irrigation, livestock watering, vehicle washing, and toilet flushing, the math is even more favorable. A 1,000 square foot garden irrigated at 0.5 gallons per square foot per week during a 20-week growing season requires roughly 10,000 gallons — less than 18% of what a 2,000 square foot standing seam roof collects annually in Nashville.
Standing seam metal with non-toxic factory finish (PVDF or SMP). The roof is the largest and most important component — its material, finish, and condition determine the quality and quantity of every drop you collect. This is the one component you cannot upgrade later without replacing the entire system.
Seamless aluminum or galvanized steel gutters, sized to handle Nashville's heaviest downpours (6" gutters recommended over standard 5" for catchment systems). Leaf screens or gutter guards at the gutter entrance prevent large debris from entering the system. Downspouts direct water from gutters to conveyance piping.
A fine mesh screen at the downspout or at the tank inlet removes leaves, twigs, insects, and coarse particulate before water enters the first-flush diverter or tank. Self-cleaning designs shed debris automatically with water flow.
Diverts the first volume of rainfall away from the storage tank — this first flush contains the highest concentration of dust, pollen, bird droppings, and atmospheric deposits that accumulated on the roof since the last rain. See Section VII for sizing and details.
PVC, HDPE, or similar food-grade piping carries filtered, diverted water from the downspout system to the storage tank. "Dry" systems (pipes drain completely between rain events) are preferred over "wet" systems (pipes hold standing water) to prevent stagnation and mosquito breeding.
Above-ground polyethylene tanks (most common), underground concrete or fiberglass cisterns, or metal tanks store collected water. Tanks must be opaque (no light penetration to prevent algae), sealed against insects and debris, and equipped with overflow plumbing. See Section VIII for sizing.
Overflow piping directs excess water away from the foundation when the tank is full. Distribution is by gravity (if tank is elevated) or pump (most systems). For garden irrigation, a simple spigot or gravity-fed drip line may suffice. For indoor use, a pump and pressure tank deliver water at household pressure through dedicated non-potable plumbing or — with treatment — the main supply.
Multi-stage filtration (sediment → carbon → UV sterilization or chlorination) is required for any rainwater used for drinking, cooking, or bathing. Treatment systems must be designed for the specific contaminants present and maintained on a regular schedule. All potable rainwater systems should be tested periodically by a qualified laboratory.
For a 2,000 sq ft roof: minimum 20-gallon first-flush diverter
For heavily treed properties or areas near construction: increase to 25–50 gallons per 1,000 sq ft
First-flush diverters work by filling a sealed chamber before allowing water to pass to the tank. Once the chamber fills (diverting the dirty first gallons), a ball valve seals it and all subsequent water flows to the tank. After the rain stops, a slow-release drain empties the chamber over 24–48 hours so it is ready for the next event. This is a passive system with no power or moving electronics — just gravity, a ball, and a drip valve.
Most Nashville residential systems start with 1,000–5,000 gallons of storage for garden and non-potable use. Homesteaders and rural properties targeting whole-house supply typically install 10,000–20,000 gallons or more, often with a backup connection to municipal or well water for extended dry periods.
Both systems collect rainwater effectively. The difference is in water quality, long-term maintenance, and suitability for potable use. Standing seam's smooth, fastener-free surface produces cleaner initial runoff and eliminates the ongoing maintenance concern of degrading rubber washers on exposed screws. For non-potable uses like garden irrigation, either system works well. For potable use, standing seam is the clear choice — and the only metal roof type specifically endorsed by ARCSA.
Plain galvanized steel (zinc-coated) can leach elevated levels of zinc into collected rainwater — a concern for both plant health and potable use. Galvalume (55% aluminum / 45% zinc alloy) leaches significantly less and is the standard substrate for modern standing seam panels. If rainwater collection is a priority, specify Galvalume substrate with a factory-applied PVDF or SMP finish — which is exactly what we install as standard on every standing seam roof.
Standing seam roof → seamless gutters with leaf screens → first-flush diverter (20–40 gallon) → 1–4 rain barrels or small poly tank (55–330 gallons) → gravity-fed garden hose or drip irrigation. Ideal for raised beds, flower gardens, container plants. Minimal installation, no pump required if tank is elevated.
Standing seam roof → 6" seamless gutters with pre-filters → first-flush diverters at each downspout → 1,500–5,000 gallon poly tank (above-ground) → small pump → drip irrigation or sprinkler system. Handles large gardens, landscape beds, and moderate outdoor water needs through Nashville's growing season.
Full roof collection → oversized gutters → pre-filtration → first-flush → 5,000–10,000 gallon tank or underground cistern → pump and pressure tank → dedicated non-potable plumbing for toilets, laundry, outdoor use. Reduces municipal water consumption 40–60%. Requires separate plumbing runs clearly marked "non-potable."
Complete roof-to-tap system: full standing seam roof collection → pre-filtration → first-flush → 10,000–20,000+ gallon storage (often underground cistern) → multi-stage treatment (sediment filtration → activated carbon → UV sterilization or chlorination) → pressure tank → whole-house supply. Backup municipal or well water connection recommended. Requires periodic water quality testing. Most common on rural properties and homesteads outside municipal water service areas.
We install the standing seam metal roof — the catchment surface that makes the entire system work. We can coordinate with rainwater system installers for the below-roof components (gutters, diverters, tanks, plumbing, treatment), or you can work with the installer of your choice. We ensure the roof is designed and installed to maximize collection efficiency for your specific system requirements.
The vast majority of residential rainwater systems in Nashville are non-potable — garden irrigation is by far the most common use, followed by landscape watering and toilet flushing. These applications require minimal treatment beyond first-flush diversion and basic filtration, and they represent the fastest return on investment because outdoor water use is pure consumption (it does not cycle back through municipal treatment).
Potable systems are more complex, more expensive, and require ongoing maintenance and testing — but they are proven, functional, and increasingly common on rural Tennessee properties. The University of Tennessee has implemented rainwater harvesting on campus facilities for toilet flushing and laundry, demonstrating institutional confidence in the technology.
This information is provided for general educational purposes and does not constitute legal advice. Laws and regulations can change. Consult local building authorities and, where appropriate, a licensed plumber or attorney for guidance specific to your property and intended system.
If you have an existing roof and want to start collecting rainwater, have the runoff tested before committing to a large storage system. A basic water quality test from a certified lab costs $50–$150 and tells you exactly what you are working with. If the roof surface is problematic, NSF-certified elastomeric coatings can be applied over existing roofing to create a safe collection surface — but starting with standing seam metal eliminates the problem entirely.
All costs are approximate ranges as of early 2026 and vary by system size, configuration, site conditions, and local labor/material costs. Roof pricing varies by panel profile, gauge, finish, and project complexity. Contact us for a project-specific roof estimate. Below-roof system pricing is provided for general reference — we recommend obtaining quotes from qualified rainwater system installers for those components.
Yes. Rainwater harvesting is legal in Tennessee with no state-level restrictions on collection volume, storage capacity, or end use. SB 2417 / HB 1850 supports green infrastructure including rainwater harvesting. If you plan to connect a system to indoor plumbing, the Tennessee Plumbing Code applies and you may need permits for that connection. The collection itself is unrestricted.
A 2,000 square foot standing seam roof in Nashville can theoretically collect approximately 56,800 gallons per year — about 155 gallons per day on average. The formula is: rainfall (inches) × roof area (sq ft) × 0.623 × efficiency (0.95 for standing seam). Real-world collection after first-flush diversion and system losses is typically 75–90% of the theoretical maximum.
With proper treatment, yes. Potable rainwater systems require multi-stage treatment — typically sediment filtration, activated carbon filtration, and UV sterilization or chlorination — plus periodic water quality testing by a certified laboratory. Standing seam metal with a non-toxic factory finish is the ARCSA-recommended catchment surface for potable use. Most Nashville residential systems use collected rainwater for non-potable purposes (garden, landscape, laundry, toilets) which require much less treatment.
Three reasons: collection efficiency (95%+ vs. 85–90% for tile and 80–90% for shingles), water quality (smooth non-porous surface with no granules, petroleum, organic material, or exposed fasteners degrading into the runoff), and longevity (50–60+ year collection surface vs. 20–30 years for shingles). Standing seam is the only conventional roofing material recommended by ARCSA for potable rainwater collection.
A passive device that captures the first volume of rainfall from each storm — the dirtiest water containing accumulated dust, pollen, bird droppings, and debris from the roof surface. After the diverter chamber fills (typically 10–20 gallons per 1,000 sq ft of roof), a ball valve seals it and clean water flows to the tank. A slow-release drain empties the chamber between storms so it is ready for the next event.
All tank openings must be screened with fine mesh (no larger than 1/16") to prevent mosquito entry. Overflow pipes should have screen covers. First-flush diverter chambers must drain completely between events (no standing water). Properly sealed and screened tanks do not breed mosquitoes — the concern is valid but the solution is straightforward with correct system design.
Possibly. If your existing metal roof has a factory-applied finish in good condition (no significant rust, peeling, or coating failure), it can be an effective collection surface. Have the runoff tested to determine water quality. If the roof is aging or the finish is deteriorating, a new standing seam roof provides the optimal collection surface and resets the 50–60 year clock on both roof protection and water collection.
It depends on your use. For garden irrigation: 500–3,000 gallons covers most Nashville gardens. For non-potable indoor use (toilets, laundry): 2,500–10,000 gallons. For whole-house potable supply: 10,000–20,000+ gallons. Size your tank to cover your consumption through Nashville's longest typical dry stretch (2–3 weeks in early fall) rather than trying to store an entire year's collection.
We install the standing seam metal roof — the catchment surface that determines the quality and efficiency of every drop collected. We also install seamless gutters designed for collection systems. For below-roof components (tanks, piping, filtration, treatment, pumps), we coordinate with qualified rainwater system installers or you can work with the provider of your choice. We ensure the roof is optimized for your collection goals.
Call us for a consultation. We will discuss your rainwater collection goals, assess your roof (existing or planned), walk through standing seam options and sizing, and — if you are building a complete system — help connect you with qualified rainwater system installers in the Nashville area. Whether you are adding a rain barrel to a garden shed or designing a whole-house potable system for a rural homestead, the roof is where it all starts.
Nashville gives you 48 inches of rain a year. A standing seam metal roof catches 95% of it — cleaner, faster, and longer than any other roofing material on earth. Whether you are watering a garden or building a whole-house system, the roof is where it all begins.