Rainwater Harvesting and Greywater Use for Idaho Landscapes

Published: January 15, 2025 | By: Lawn Care Kuna Team | Category: Irrigation

Tags: rainwater harvesting, greywater, water conservation, sustainable landscaping, alternative water, idaho irrigation

Alternative Water Sources for Idaho Landscapes

In Southwest Idaho's semi-arid climate, where average annual rainfall barely reaches 12 inches and summer months bring hot, dry conditions, water-conscious homeowners increasingly explore alternatives to traditional irrigation. Rainwater harvesting captures precipitation for landscape use, while greywater systems redirect gently-used household water to outdoor irrigation. Both approaches reduce demand on municipal or well water supplies, lower water bills, and contribute to sustainable landscape management.

For Treasure Valley homeowners committed to water conservation, understanding these alternative water sources—including their benefits, limitations, installation requirements, and legal considerations in Idaho—helps determine whether they're appropriate additions to your landscape water management strategy. While neither approach replaces conventional irrigation entirely in our climate, both can meaningfully reduce water consumption and costs.

Rainwater Harvesting in Idaho

The Potential and Limitations

Idaho's rainfall pattern presents both opportunities and challenges for rainwater harvesting:

Seasonal distribution: Most precipitation falls October through May; summers are notably dry
Winter collection challenges: Snow and freezing temperatures limit winter harvesting
Peak demand mismatch: Highest irrigation needs occur when rainfall is lowest
Storage requirements: Bridging seasonal gaps requires substantial storage capacity

Despite these challenges, rainwater harvesting makes sense for specific applications in Idaho landscapes, particularly supplementing irrigation during spring and fall shoulder seasons when some rainfall occurs and irrigation demands are moderate.

How Much Water Can You Collect?

Rainwater collection potential depends on catchment area and local rainfall:

Basic formula: Collection (gallons) = Roof area (sq ft) × Rainfall (inches) × 0.623 × Collection efficiency (typically 75-90%)

Roof Area	Per 1" of Rain	Annual Potential (12" average)
1,000 sq ft	~560 gallons	~6,700 gallons
1,500 sq ft	~840 gallons	~10,000 gallons
2,000 sq ft	~1,120 gallons	~13,400 gallons
2,500 sq ft	~1,400 gallons	~16,800 gallons

Compare these volumes to irrigation needs: a 5,000 sq ft lawn in the Treasure Valley might require 80,000-100,000 gallons annually. Rainwater alone won't meet this demand, but can meaningfully supplement other sources.

Rainwater Harvesting System Components

Basic rainwater harvesting systems include:

Catchment surface: Typically the roof. Material affects water quality—metal and tile are ideal; asphalt shingles are acceptable for landscape irrigation
Gutters and downspouts: Collect and direct water. Size appropriately for local rainfall intensity
First-flush diverter: Diverts initial rainfall that washes debris and contaminants from the roof
Filtration: Screens and filters remove leaves, debris, and sediment
Storage tanks: Hold collected water. Size depends on collection goals and available space
Distribution: Gravity feed for simple systems; pumps for pressurized delivery

Storage Tank Sizing

Tank sizing balances collection capacity, irrigation needs, and cost:

Small systems (50-100 gallons): Simple rain barrels for spot watering and container gardens
Medium systems (250-500 gallons): Useful for garden beds and supplemental irrigation
Large systems (1,000+ gallons): Meaningful contribution to landscape irrigation, requiring significant investment
Cistern-scale (5,000+ gallons): Can substantially supplement irrigation but represents major investment

Installation Considerations

Successful rainwater systems require:

Adequate roof area: Larger catchment means more collection potential
Suitable tank location: Level ground, structural support if elevated, frost protection
Overflow management: Excess water must drain away from foundations
Winterization: Idaho winters require tank drainage or frost protection
Mosquito prevention: Screens on all openings prevent breeding
Connection to landscape: Integration with existing irrigation or separate distribution

Greywater for Landscape Irrigation

What Is Greywater?

Greywater is gently-used water from bathroom sinks, showers, bathtubs, and washing machines. It's distinguished from blackwater (toilet waste) and kitchen wastewater (which contains fats and food particles). Properly managed greywater can safely irrigate ornamental landscapes.

Idaho Greywater Regulations

Idaho regulates greywater systems through the Division of Environmental Quality. Key requirements include:

Systems must follow the International Plumbing Code provisions adopted in Idaho
Greywater must be used for subsurface irrigation only (no surface ponding or spraying)
Food gardens require specific separation from greywater application
Permits may be required depending on system size and local jurisdiction
Systems cannot discharge to surface water or groundwater
Overflow must connect to the septic or sewer system

Local jurisdictions may have additional requirements—check with your city or county building department before installation.

Greywater Volume Potential

A typical household generates substantial greywater:

Showers and baths: 10-25 gallons per use
Bathroom sinks: 1-2 gallons per use
Washing machines: 15-40 gallons per load

A family of four might generate 40-80 gallons of usable greywater daily—potentially 12,000-24,000 gallons during the irrigation season. This represents meaningful irrigation supplementation.

Greywater System Types

Systems range from simple to sophisticated:

Laundry-to-landscape: Simplest system, redirects washing machine water directly to subsurface irrigation through mulch basins. Often doesn't require permit in Idaho.
Branched drain systems: Gravity-fed distribution through branching pipes to multiple landscape areas. Requires careful design for proper flow splitting.
Pumped systems: Collect greywater in tanks and pump to irrigation areas. Allows greater flexibility in distribution but requires more equipment.
Treatment systems: Filter and treat greywater before distribution. Required for some applications and provides better water quality.

Safe Greywater Practices

Proper greywater use requires attention to safety:

Subsurface only: Greywater must soak into soil, not pond on surface or contact people
Avoid food gardens: Don't use greywater on vegetables or fruits eaten raw
Use "greywater-safe" products: Avoid bleach, boron, sodium-heavy detergents
Rotate application areas: Prevent salt and residue buildup in one location
Don't store: Use greywater within 24 hours to prevent bacterial growth
Divert when inappropriate: Divert to sewer during illness, when washing diapers, or using harsh chemicals

Combining Alternative Water Sources

Integrated Water Strategy

The most effective approach combines multiple water sources:

Municipal/well water: Primary irrigation source during peak summer demand
Rainwater: Supplements irrigation during shoulder seasons when some rain falls
Greywater: Provides consistent daily volume for designated landscape areas
Smart irrigation: Optimized sprinkler systems maximize efficiency of all water sources

Landscape Design for Alternative Water

Landscapes can be designed to maximize alternative water use:

Group plants by water needs, directing limited alternative water to appropriate areas
Create greywater-specific zones with tolerant plants and mulch basins
Position rainwater collection near garden beds for easy distribution
Use mulch extensively to reduce overall water needs
Select drought-tolerant plants that can survive on reduced irrigation

Practical Considerations for Idaho Homeowners

Cost-Benefit Analysis

Evaluate alternative water systems realistically:

Simple rain barrels: Low cost ($50-150), limited volume, good for containers and small gardens
Larger rainwater systems: Moderate to high cost ($500-5,000+), useful supplementation but limited by Idaho's rainfall
Laundry-to-landscape greywater: Low cost ($200-500), consistent volume, relatively simple installation
Complete greywater systems: Higher cost ($1,500-5,000+), more complex but greater capacity

Payback periods depend on local water costs and system complexity. In the Treasure Valley, where water costs remain relatively low, environmental motivation often outweighs financial return.

Winter Considerations

Idaho winters require seasonal management:

Rainwater tanks must be drained or protected from freezing
Greywater systems may need winterization or diversion to sewer
Exposed pipes require freeze protection
Spring activation should include system inspection and cleaning

Maintenance Requirements

Alternative water systems need regular attention:

Clean gutters and screens before and during rain season
Inspect tanks and connections for leaks and damage
Clear any debris from distribution systems
Monitor soil in greywater areas for salt or pH changes
Service pumps and filters as required

Getting Started

Start Small

Beginning with simple systems allows learning without major investment:

Install one or two rain barrels for container watering
Try a laundry-to-landscape greywater setup for one landscape area
Evaluate results before expanding systems

Professional Consultation

Complex installations benefit from professional guidance:

Plumbers for greywater system installation
Irrigation specialists for integration with existing systems
Local code officials for permit requirements
Landscape professionals for plant selection and layout

Lawn Care Kuna provides comprehensive landscape and irrigation services throughout Kuna, Meridian, Boise, Eagle, Star, and the Treasure Valley. While we don't install rainwater or greywater systems, our irrigation services help maximize efficiency of all water sources, and our landscape expertise can help design water-wise landscapes that work with alternative water systems. Request a free consultation or contact us to discuss sustainable landscape management for your property.

Frequently Asked Questions

Is rainwater harvesting legal in Idaho?

Yes, rainwater harvesting is legal in Idaho for residential use. Unlike some Western states with complex water rights restrictions on rainwater, Idaho allows homeowners to collect precipitation falling on their property for domestic landscape use without permits or water rights. However, collected rainwater should be used on the property where it's collected—selling or transporting rainwater off-site may have different legal considerations. Local jurisdictions may have requirements for tanks or cisterns above certain sizes, particularly regarding structural support, setbacks, or appearance. Check with your local building department about any tank size thresholds that trigger permitting or review requirements. Overall, Idaho is relatively friendly to residential rainwater collection.

Can I use greywater on my vegetable garden?

Greywater use on food gardens requires caution and may be restricted. Idaho regulations generally require greywater to be applied subsurface (not sprayed or ponded), which protects edible plant parts from contact with greywater. For vegetables eaten raw (lettuce, tomatoes, peppers), greywater is typically not recommended even with subsurface application because some contact with edible portions is possible. Root vegetables harvested from soil may also contact greywater residues. Fruit trees and bushes where greywater doesn't contact edible portions are generally acceptable. For vegetable gardens, use conventional irrigation sources and reserve greywater for ornamental landscapes. If you do use greywater near food gardens, maintain substantial separation distance and never allow greywater to contact edible plant parts.

How much can I realistically save with rainwater harvesting in Idaho?

In the Treasure Valley's semi-arid climate, rainwater harvesting provides supplemental rather than primary irrigation. With 12 inches of annual rainfall and irrigation needs of 40+ inches during the growing season, rainwater alone cannot meet landscape water demands. Realistic expectations: a 2,000 sq ft roof might collect 13,000 gallons annually—roughly 15-20% of a typical lawn's annual water requirement. However, rainwater's value is higher for specific applications: hand watering containers and gardens, supplementing shoulder-season irrigation when some rain falls naturally, and reducing peak-season municipal water use. Financial savings depend on local water costs—at Treasure Valley municipal rates, 13,000 gallons might save $40-80 annually, representing long payback periods for system investments. Environmental benefits and self-sufficiency motivations often exceed financial returns.

What household products can't be used if I'm collecting greywater?

Greywater systems require attention to the products draining into them. Avoid: chlorine bleach (damages plants and soil microbes); boron-containing products (boron accumulates in soil and damages plants); high-sodium products (sodium damages soil structure over time); antibacterial soaps with triclosan or similar compounds; harsh chemical cleaners; and products labeled toxic to aquatic organisms. Use instead: liquid castile soaps; plant-based biodegradable detergents; chlorine-free oxygen bleach; low-sodium products; and products marketed as 'greywater-safe' or 'biodegradable.' For laundry, choose liquid detergents over powders (which often contain more sodium and fillers). Read ingredient labels—avoid anything listing sodium or boron compounds. When using products incompatible with greywater, divert that water to the sewer instead of the landscape.

Do I need a permit to install a rainwater or greywater system?

Permit requirements vary by system type and local jurisdiction. Rainwater: Simple rain barrels rarely require permits. Larger tanks or cisterns may require permits if they exceed certain volumes, need structural support, or require plumbing connections. Check with your local building department about thresholds—commonly 500-1,000 gallons triggers review. Greywater: Idaho follows International Plumbing Code provisions that allow simple 'clothes washer system' installations (laundry to landscape) without permits in many jurisdictions if they meet specific criteria. More complex systems involving multiple fixtures, pumps, or tanks typically require plumbing permits. Some jurisdictions require all greywater systems to be permitted. Contact your local building department before installation—requirements vary between cities and counties in the Treasure Valley. Professional installation typically includes permit acquisition.

Can rainwater or greywater damage my landscape or irrigation system?

Both water sources require management to avoid problems. Rainwater concerns: Roof runoff may contain debris, bird droppings, or roofing material residues—use first-flush diverters and filtration. Asphalt shingle runoff contains some petroleum compounds but is generally acceptable for landscape irrigation. Metal or tile roofs provide cleanest water. Stored rainwater can breed mosquitoes without proper screening. Greywater concerns: Detergent residues can raise soil pH and sodium levels over time—use appropriate products and rotate application areas. Greywater can contain pathogens—subsurface application prevents human contact. Salt accumulation in drip systems or soil requires monitoring. Neither source typically damages properly designed irrigation systems, though greywater should bypass filtration systems designed for clean water. Both require winterization to prevent freeze damage in Idaho's climate.