As a Denver-based custom builder working on clients’ own lots, we incorporate rainwater harvesting as a site-specific system rather than an add-on. In the Front Range climate — relatively low annual precipitation with strong seasonal swings and regular freeze/thaw — effective capture depends on roof area and orientation, run-off routing, and freeze protection. We begin every project by assessing the lot, roof plan and landscape needs so the system is sized and sited to maximize capture for irrigation, outdoor use, and available non‑potable household uses while meeting local codes and HOA rules.
A functional system includes coordinated roof gutters and downspouts, first‑flush diverters and leaf screens, a storage tank (aboveground or buried), filtration and treatment appropriate to the intended use, a pressure pump and controls, and an overflow tied into approved drainage. A simple sizing rule you can use is: rainfall (inches) × roof area (sq ft) × 0.623 = gallons potentially captured; from that we compare storage options — small yard-focused installations commonly use 500–2,500 gallon tanks, while whole‑house non‑potable systems often run 5,000 gallons or more. Underground tanks require excavation, compaction and structural review; exposed tanks need frost protection or insulated piping and heat trace in our climate. All systems also require backflow prevention, accessible maintenance points for sediment flushing, and properly permitted overflow connections.
To make rainwater harvesting part of the build rather than a retrofit, we coordinate the plumbing, electrical and civil work during design so pumps, mechanical equipment, tank access and irrigation zones are built into the foundation and sitework schedules. That reduces cost and avoids awkward routing later: rough‑ins for non‑potable plumbing, a reserved mechanical alcove for controllers and pumps, and landscaping plans matched to the storage capacity all get handled in the construction documents and permit set. At RKM Homes we manage those trades and the permitting process, size systems to your water‑use goals, and specify freeze‑resistant installations and maintenance access so the system performs reliably year‑round on your lot.
How do I size a rainwater harvesting system for my custom home?
Start by inventorying the non‑potable uses you actually want the system to support — toilets, laundry, irrigation, and vehicle washing are the usual candidates. Make a conservative estimate of daily demand for each use: check fixture labels (toilets often 1.28–1.6 gal/flush, washing machines 15–40 gal/load, showers measured in gpm) or track a week of usage to get real numbers, then sum to a daily non‑potable demand. For irrigation, convert landscape area to water need using the simple rule that 1 inch of water on 1,000 sq ft ≈ 623 gallons (or 0.62 gallons/sq ft per inch); multiply by the seasonal irrigation depth you plan to apply and divide by the number of irrigation days to estimate daily irrigation demand.
Estimate how much water you can realistically capture from your roof by using this formula: capture (gal) = roof area (sq ft) × rainfall (in) × 0.62 × runoff coefficient. Use a runoff coefficient of about 0.9–0.95 for metal or tile roofs and 0.75–0.9 for asphalt shingles. For example, a 4,000 sq ft roof with a 0.9 coefficient yields roughly 4,000 × 1 in × 0.62 × 0.9 ≈ 2,232 gallons per 1‑inch storm. Decide how many days of autonomy you want (7–14 days is common for non‑potable systems) and size storage to meet demand during dry intervals: if your calculated daily non‑potable need is 200 gal/day and you want 10 days of storage, aim for ~2,000 gallons of usable storage, then compare that to capture estimates to see if you’ll refill that volume often enough.
Make sizing a collaborative part of the schematic design phase so roof area, roof material choices and landscape demands can be adjusted to improve capture-to-demand balance. Run a simple spreadsheet model with local monthly rainfall averages and your daily demand to see worst‑month deficits; if capture is seasonal, you may need larger tanks or to limit the system to specific uses. Also factor in practical constraints early — available space, budget and the structural implications of filled storage — and plan for modular tanks if you want to start small and expand later rather than guessing a one‑time “perfect” size.
What catchment, roofing materials, gutters and conveyance design should I choose for rainwater harvesting on a custom home?
As a custom home builder I start roof design with catchment in mind: the smoothness, slope and material of the roof determine how clean the water will be and how easy it is to channel into gutters. Standing‑seam metal is the easiest and cleanest option — it sheds quickly, has minimal particulates and lasts decades — while asphalt shingles shed granules that can clog screens and increase filtration needs. Avoid copper or roofs treated with heavy preservatives if you intend to use water for landscaping; clay or slate tile can work but require careful detailing at valleys and mortar joints to prevent sediment. When choosing your roof, ask for product data on runoff composition and tell your roofer we’re planning rainwater capture so flashing and valley details are executed to minimize debris traps.
Gutter selection and placement are things I detail on the plans so they’re not an afterthought. For most custom homes we specify 5″ K‑style or 6″ box gutters with downspouts sized 3″–4″ (or larger where roof runs are long), located to keep run lengths to tanks as short and gravity‑fed as possible. Gutters should be installed with a consistent slope (roughly 1/16″–1/8″ per foot) toward the designated downspouts, and boxed or seamless aluminum with baked enamel finish avoids corrosion and paint failure. Include wide‑mesh leaf guards or micro‑screens at the gutter inlets and accessible clean‑outs at roof valleys so debris can be removed during routine maintenance without opening the system.
Conveyance design is where plumbing and civil coordination meet the roof work: specify screened downspout inlets, a first‑flush diverter to discard the initial roof wash, and smooth, UV‑resistant piping (HDPE or PVC in buried runs; aluminum or copper only if compatible with water use) with an accessible slope to the collection point. In snowy climates like Denver, plan for heated or pitched gutters/scuppers and locate downspouts to avoid ice buildup at entrances — bury pipe below frost line or route it to a tank location that minimizes exposed pipe runs. During construction coordinate roof layout, gutter fascia details and underground utility trenches so the capture system is integrated into framing and grading rather than patched in later.
What are my rainwater storage options, where should tanks be sited, how do I size capacity, and how are tanks integrated with my home’s foundation?
As a custom home builder I balance budget, aesthetics and site constraints when choosing storage: above‑ground polyethylene or galvanized tanks are the quickest and cheapest to install and are fine for 300–5,000 gallons where visibility and landscaping matter; fiberglass or steel offer slimmer footprints if you need a narrow aesthetic; concrete or factory‑built bolted steel cisterns are common for large capacities or buried systems because they resist soil loads. Practically, above‑ground tanks can be placed on a compacted gravel pad and hooked up quickly, while buried tanks need a structural base, careful bedding, and heavy equipment for delivery and backfill. When you pick a material and size, factor in access for cleaning/manholes, pump and filter cabinets, freeze protection for our climate (insulated vaults or frost‑protected pump locations), and whether future expansion will be desired—modular tanks make staged growth easier.
Siting decisions are driven by gravity vs. pumped systems, truck/crane access for installation, frost line and drainage, and the relationship to the house. I try to keep cisterns outside the primary foundation footprint and place them on their own engineered pad a few feet from the house to avoid transmitting loads or hydrostatic forces into the foundation; if the client wants a tank under a garage or slab that is possible, but it requires an engineered vault, waterproofing, and coordination with the garage slab reinforcement so the tank does not carry building loads. You also need to plan clearances for service (typically a 3–6 ft service zone for pump access), route overflow away from foundations, and ensure that piping penetrations through any foundation wall are detailed with sleeves and isolation to avoid settlement or leakage issues.
For capacity and structural integration, use a simple capture formula: roof catchment area (ft²) × expected seasonal rainfall (inches) × 0.623 = gallons captured per season (or per inch of rain). For example, a 2,000 ft² roof yields about 1,246 gallons per inch of rain. Decide your storage target by matching that capture to your demand (irrigation/indoor non‑potable loads) and the longest expected dry spell—urban homes commonly end up with cisterns in the 1,200–5,000 gallon range; estates often design 10,000+ gallons. Any below‑grade tank requires an engineered foundation: design teams will size a reinforced concrete pad or ring beam to support the tank and account for live/saturated soil loads and seismic or frost actions. Early coordination with your structural engineer and plumber is essential so slab thickness, rebar layout, conduits, and access manways are built into the scope rather than retrofitted, which is far more costly.
How do I plumb harvested rainwater for potable and non‑potable uses while preventing cross‑connections and meeting local code and permitting requirements?
Decide during design whether harvested rain will be used for non‑potable loads (toilets, irrigation, laundry) or treated to potable standards — that choice drives the entire plumbing approach. For non‑potable use we install a completely separate distribution loop with dedicated pumps, pressure tank, and fixtures on purple‑marked piping; this loop is isolated from the domestic potable system and sized at rough‑in with its own valves and access points so it can be maintained without disturbing the domestic water system. If the owner wants potable reuse, plan for a treatment train (pre‑filtration, cartridge or multimedia filter, UV or chlorination, and often post‑storage polishing) and additional monitoring hardware; potable reuse almost always requires a dedicated potable pump, separate sensor/alarms, and plumbing that can be inspected and disinfected to public‑health standards.
Cross‑connection control is non‑negotiable and is enforced differently in every jurisdiction — typical requirements we build to include physical separation (air gaps) at fill points, approved backflow prevention assemblies (RPZ or DCVA) on any connection where rainwater and potable systems could interact, and check valves plus lockable isolation valves on the rainwater supply. We size and locate the RPZ per the inspector’s spec, create inspection ports and testable sections, and use purple piping and permanent signage to prevent accidental cross‑ties. Expect mandatory annual backflow device testing by a certified tester and keep test reports on file; never allow a direct tie into the domestic potable mains without documented treatment, permitting, and an approved backflow control plan.
Permitting and code compliance should be started early — we submit plumbing schematics, treatment specifications, and a cross‑connection control plan with the building permit or a separate plumbing permit depending on your municipality. As your builder I coordinate with the licensed plumber to include required details (pipe materials, labeling, RPZ locations, tank setbacks, and foundation/structural notes) so plan review is smooth; you should budget for plan‑review fees, possible engineering for tank foundations, and lab water sampling if potable reuse is proposed. Practical homeowner actions: confirm the builder will obtain permits and signoffs in the contract, request a copy of approved drawings and backflow test certificates for your records, and schedule the plumbing rough‑in and backflow inspection in the construction timeline because those inspections are milestones that affect final occupancy and system commissioning.
What filtration, treatment, maintenance, and backup systems will my rainwater harvesting system need?
For non‑potable uses like irrigation and toilet flushing, we typically specify a staged approach: roof screens and leaf guards at the gutter, a first‑flush diverter to shed the very dirty initial runoff, a sediment/micron mesh filter (100–500 µm) ahead of the pump, and a cartridge filter (5–50 µm) sized for final particulate removal. If you want household potable use, add an activated‑carbon filter for taste/organics and a UV disinfection unit rated for the flow; some clients prefer a small automatic chlorination system for residual protection in long runs. All treatment equipment should be mounted in a conditioned space (mechanical room or garage) with easy access, drain points, and labeled isolation valves so you can service, bypass or winterize components without shutting down the whole house.
Maintenance planning is simple but non‑negotiable: clear gutters and screens seasonally (more often if you have trees), empty or service the first‑flush diverter after heavy leaf fall, change cartridge filters on a schedule based on rainfall and turbidity (commonly every 3–12 months), replace UV lamps annually and clean quartz sleeves, and inspect/clean the tank every 1–3 years to remove settled sludge. We install a manway or service hatch and a low‑point drain to make tank cleaning practical; include a sample port to test water quality before you connect it to sensitive fixtures. For homeowners, keep spare cartridges and a basic maintenance log; plan and budget for an annual contractor inspection so filters, valves, pumps and seals get a professional check.
Redundancy and fail‑safe design keep the system reliable: we include an automatic municipal‑water changeover valve to maintain continuous supply for critical indoor uses, pressure/level sensors with audible or app alerts, and at least one run‑of‑spare filter or a parallel filter bank so you can service one train while the other remains online. For sites with power‑outage risk, a small UPS for control electronics and a generator or battery backup for the pump can preserve water for essentials; for irrigation-only systems we often rely on simpler battery float switches and a manual municipal bypass. Ask your builder to show you the isolation points, demonstrate the automatic changeover operation, and provide a one‑page maintenance schedule so you can keep the system operating efficiently and avoid emergency service calls.