Rainwater Harvesting System Product

Overview

Rainwater harvesting systems capture precipitation from roof surfaces, filter and store it in large tanks, and distribute it for non-potable uses—landscape irrigation, toilet flushing, laundry, and vehicle washing. By reducing mains water consumption 30–60% in residential and commercial applications, these systems lower utility bills and municipal peak demand. Modern systems include automatic switchover to mains water supply if the tank depletes, eliminating the risk of dry taps during drought.

Rainwater harvesting is particularly valuable in arid regions, areas with metered water charges, or buildings with large roof areas (hotels, warehouses, schools). Typical payback periods are 5–10 years in water-scarce climates; compliance with local stormwater management ordinances (which favor on-site retention) further justifies the investment.

How it works

Rainfall runs from the roof into [[rainwater-harvesting-system-roof-guttering|gutters and downspouts]], where a [[rainwater-harvesting-system-first-flush-diverter|first-flush diverter]] automatically discards the first 15–30 liters of contaminated roof runoff (bird droppings, dust, leaves) directly to storm drainage. Clean water then flows through a [[rainwater-harvesting-system-hose-strainer|strainer]] and fills the [[rainwater-harvesting-system-storage-tank|storage tank]].

When rainwater demand begins (tap opened for toilet or irrigation), a [[rainwater-harvesting-system-pump-circulation|pump]] draws from the tank, pushes water through a [[rainwater-harvesting-system-filter-unit|multi-stage filter]], and supplies the distribution network at 40–60 PSI. A [[rainwater-harvesting-system-level-sensor|tank level sensor]] continuously monitors volume. If the tank falls below minimum level (e.g., 10% capacity), the [[rainwater-harvesting-system-control-unit|control unit]] de-energizes the rainwater side of a [[rainwater-harvesting-system-manifold-valves|3-way solenoid valve]], automatically switching supply to [[rainwater-harvesting-system-check-valve-mains|mains water]] without interruption. When the tank refills, rainwater supply automatically restores.

Components & Design

Roof Catchment & Pre-filtration

The [[rainwater-harvesting-system-roof-guttering|gutter and downspout]] system is sized to handle the expected roof area drainage (5 inch gutter per 1000 sq ft is typical). The [[rainwater-harvesting-system-first-flush-diverter|first-flush diverter]]—a float-actuated ball valve in the downspout—sends the first ~20 liters of dirty water to nearby storm drain or splash-out, automatically closing once flow stabilizes. This removes 80% of suspended solids without manual intervention. A [[rainwater-harvesting-system-leaf-guard|leaf guard]] screen in the gutter prevents debris accumulation; annual cleaning of leaves and sediment from gutters extends system life.

Storage Tank

The [[rainwater-harvesting-system-storage-tank|tank]] is a sealed 500–5000 liter polyethylene (high-density plastic) or reinforced concrete vessel. Polyethylene tanks are lighter and faster to install; concrete offers superior durability and UV resistance for above-ground siting. The tank includes an [[rainwater-harvesting-system-tank-inlet|inlet distribution pan]] (sloped to direct inflow to the sump, minimizing sediment suspension), an [[rainwater-harvesting-system-tank-overflow|overflow port]] (typically 2 inch discharge piped to storm drainage or surface infiltration), a [[rainwater-harvesting-system-tank-access-cover|lockable inspection cover]] (600 mm diameter) to prevent mosquito entry and contamination, and a [[rainwater-harvesting-system-tank-drain-valve|drain valve]] at the sump for sediment purging.

A [[rainwater-harvesting-system-tank-vent-filter|carbon vent breather]] allows tank pressure equalization as water enters and drains, while preventing odor escape. The tank interior is kept dark (opaque plastic exterior) to discourage algae growth. Annual maintenance includes inspection of the access cover gasket and vent filter, and gravity draining of accumulated sediment (typically 1–3 liters) through the sump drain.

Filtration

The [[rainwater-harvesting-system-filter-unit|multi-stage filter]] removes suspended solids in two steps: a [[rainwater-harvesting-system-sediment-cartridge|20–50 micron sediment cartridge]] traps sand and silt; a [[rainwater-harvesting-system-carbon-cartridge|granular activated carbon cartridge]] removes residual chlorine (if mains backup is chlorinated), taste, and odor. The [[rainwater-harvesting-system-backflush-valve|multiport valve]] allows isolation and reverse-flow cleaning when pressure drops 15 PSI across the cartridge, extending cartridge life to 6–12 months at typical residential flow rates. The [[rainwater-harvesting-system-pressure-gauge|inline pressure gauge]] indicates when backflushing is needed.

Pump & Circulation

The [[rainwater-harvesting-system-pump-circulation|pump assembly]]—typically a 0.5–1 HP centrifugal pump—is either submersible (mounted inside the tank, space-saving) or surface-mounted beside the tank (easier servicing). Submersible pumps are flooded suction and require no priming; surface pumps must be installed below tank outlet or equipped with a priming valve. The pump motor has [[rainwater-harvesting-system-pressure-switch|pressure switch]] set to 40 PSI start and 60 PSI stop; the switch energizes the motor when a fixture opens and pressure drops, and de-energizes once the distribution line is pressurized. A [[rainwater-harvesting-system-soft-start-capacitor|soft-start capacitor]] limits inrush current, protecting the motor and reducing audible shock at startup.

Control & Switchover

The [[rainwater-harvesting-system-control-unit|control unit]] is a small enclosure containing a [[rainwater-harvesting-system-transformer|24V transformer]], [[rainwater-harvesting-system-switchover-relay|relay]], and terminal blocks. A [[rainwater-harvesting-system-level-sensor|float or ultrasonic level sensor]] inside the tank sends a signal to the relay; when tank level drops to the low setpoint, the relay de-energizes the [[rainwater-harvesting-system-solenoid-valve|3-way solenoid valve]], which spring-shifts to route flow from mains rather than rainwater. The occupant is unaware of the switchover; pressure remains constant and supply never fails. An optional [[rainwater-harvesting-system-low-level-alarm|piezo alarm]] buzzes to alert the building manager that the tank has depleted and manual intervention may be needed (e.g., cleaning gutters to increase rainfall input).

Distribution Manifold

The [[rainwater-harvesting-system-manifold-valves|distribution manifold]] integrates the solenoid switchover valve, a [[rainwater-harvesting-system-check-valve-mains|check valve on the mains inlet]] (preventing rainwater backflow into the utility), [[rainwater-harvesting-system-isolation-valve-tank|isolation valves]] on both tank and mains sides, a [[rainwater-harvesting-system-pressure-relief|relief valve]] set to 60 PSI system maximum, and a [[rainwater-harvesting-system-drain-ball-valve|system drain valve]] for maintenance depressurization. This design allows service isolation and protects the system from water-hammer spikes when fixtures are suddenly closed.

Piping

Above-ground sections use [[rainwater-harvesting-system-pvc-pipe|Schedule 40 PVC pipe]] (100 PSI rated) or [[rainwater-harvesting-system-grp-pipe|UV-stabilized GRP fiberglass pipe]] to resist sun exposure. Buried runs below the tank use [[rainwater-harvesting-system-poly-tubing|polyethylene tubing]], which is crush-resistant and roots-resistant. [[rainwater-harvesting-system-hose-clamps|Stainless steel clamps]] secure all tubing connections.

Rainfall Yield & Sizing

Rainwater yield is calculated as 23.6 liters per 1 mm of rainfall per 1 square meter of roof area (or 1 gallon per 1 inch per 1000 sq ft). An average home with 2000 sq ft roof area in a region receiving 25 inches/year of usable rainfall would collect ~13,000 gallons/year. Subtracting 20% loss to first-flush diversion, evaporation, and filter waste leaves ~10,400 gallons usable. If the household uses 100 gallons/day for landscape irrigation and toilet flushing, the system can offset ~100 days of water, reducing mains consumption 25–30%.

Tank size is typically chosen as 10–20% of annual rainwater yield; larger tanks are uneconomical due to evaporation and extended residence time (stagnation risk). A 1000–2000 liter tank is sufficient for most residential applications.

Maintenance & Monitoring

Gutters require annual leaf and sediment removal; clogged gutters reduce collection efficiency. The [[rainwater-harvesting-system-tank-drain-valve|tank sump drain]] should be opened monthly to gravity-purge accumulated grit (typically 0.5–2 liters). Filter cartridges are replaced when the [[rainwater-harvesting-system-pressure-gauge|pressure gauge]] rises above 25 PSI (indicating 10 PSI differential restriction), or annually if flow is low. After a long drought, flush the [[rainwater-harvesting-system-filter-unit|filter]] via backflush before resuming supply if sediment may have settled.

The [[rainwater-harvesting-system-solenoid-valve|solenoid valve]] should be exercised monthly (manually switch from rainwater to mains and back) to prevent stiction. Tank exterior should be inspected annually for UV cracks (above-ground tanks); interior access cover gasket should be verified for mold or deterioration every 2 years.

Standards & Codes

Rainwater systems are classed as non-potable (unsuitable for drinking or food preparation) in most jurisdictions; plumbing code requires a [[rainwater-harvesting-system-check-valve-mains|dual-check valve or reduced-pressure principle (RP) backflow preventer]] on the mains inlet to protect the utility from contamination. Many codes also require a sign at rainwater outlets stating "Not for Drinking Water" and separate piping (often dyed purple or labeled) to prevent cross-connection with potable supply.

Stormwater management regulations in many regions encourage or mandate on-site rainwater retention; harvesting systems count toward compliance. Some municipalities offer rebates for system installation because the retained water reduces peak stormwater runoff during heavy rains.

NSF/ANSI 350 is the primary standard for rainwater treatment components; filters and materials meeting NSF 350 certification ensure safety and durability for non-potable applications.