Skip to main content

Task 2: Rainwater Harvesting - Project Template

Part of: Plan Section (Vision → Plan → Reality)
Type: Template/Playbook for Small Plot Restoration
Status: Template - Customize for Your Project

← Back to Project Hub

Purpose​

Rainwater harvesting is one of the most sustainable and cost-effective water management strategies for restoration sites. By capturing precipitation that would otherwise run off, you can supplement irrigation needs, reduce erosion, recharge groundwater, and build water security.

This is a template. Customize harvesting systems, catchment areas, and storage solutions based on your specific climate, site topography, and water needs.

🎯 Non-Negotiables (Science Consensus)​

These must be followed - they are based on scientific consensus:

  1. Water Quality Matters: Captured rainwater must be of appropriate quality for intended use. Contaminated water can harm plants, soil, and ecosystem health.

  2. Legal Compliance: All water capture and storage must comply with local water rights and regulations. This is not optional.

  3. Overflow Management: All water storage systems must have overflow management. Uncontrolled overflow can cause erosion and flooding.

  4. Maintenance Required: Water harvesting systems require maintenance to function effectively. Neglected systems fail and waste resources.

  5. Documentation: All water harvesting systems, capacities, and performance must be documented. This is essential for optimization and adaptive management.

🔀 Options & Pathways​

Pathway A: Comprehensive Professional System​

When to use: Larger projects, when water is critical, have budget, want professional design

Approach:

  • Professional hydrologist or water specialist design
  • Comprehensive active and passive systems
  • Professional installation
  • Multiple storage systems
  • Professional maintenance

Pros:

  • Most thorough and effective
  • Professional validation
  • Reliable systems
  • Suitable for challenging climates

Cons:

  • Higher cost (€5,000-50,000+)
  • Requires professional expertise
  • More infrastructure

Pathway B: DIY/Community Approach​

When to use: Limited budget, want to learn, community engagement focus, moderate needs

Approach:

  • DIY design and installation
  • Community work days
  • Simple systems (rain barrels, swales)
  • Local knowledge integration
  • Educational value

Pros:

  • Lower cost (€500-5,000)
  • Community engagement
  • Educational value
  • Accessible

Cons:

  • May be less comprehensive
  • Requires coordination
  • May need expert review
  • More maintenance

Pathway C: Passive Focus​

When to use: Moderate rainfall, want low-maintenance, natural approach preferred

Approach:

  • Focus on earthworks (swales, berms)
  • Landscape-based infiltration
  • Minimal infrastructure
  • Natural processes
  • Low maintenance

Pros:

  • Lower cost (€1,000-10,000)
  • Low maintenance
  • Natural processes
  • Works with landscape

Cons:

  • May be insufficient in very dry climates
  • Requires suitable topography
  • Less control
  • Slower to implement

Pathway D: Hybrid Approach​

When to use: Most projects - balance of active and passive systems

Approach:

  • Professional design and guidance
  • Community implementation
  • Mix of active and passive systems
  • Strategic infrastructure where needed
  • Natural methods where possible

Pros:

  • Good balance
  • Flexible
  • Cost-effective
  • Adaptable

Cons:

  • Requires coordination
  • May need ongoing consultation

📋 Implementation Steps​

Step 1: Understand Rainwater Harvesting Types​

Active harvesting (collection and storage):

  • Roof catchment systems → gutters → storage tanks/cisterns
  • Hard surface collection → filters → storage
  • Best for: Immediate water needs, irrigation, supplemental supply
  • Requires: Infrastructure investment, maintenance
  • Yields: High volume from concentrated surfaces

Passive harvesting (landscape-based infiltration):

  • Swales, berms, and basins that slow and sink water
  • Contouring landscape to capture and spread runoff
  • Best for: Groundwater recharge, erosion control, long-term soil moisture
  • Requires: Earthwork, minimal maintenance
  • Yields: Enhanced soil moisture, reduced runoff

Hybrid approach (recommended):

  • Combine both for maximum benefit
  • Active for immediate needs, passive for soil building
  • Complimentary strategies that support each other
  • Resilience through diversity

Step 2: Calculate Rainwater Harvesting Potential​

Basic formula: Catchment Area (m²) × Rainfall (mm) × 0.001 = Cubic meters (m³) or 1000 liters captured

Simplified: Catchment Area (m²) × Rainfall (mm) = Liters captured

(Accounting for ~10% loss to evaporation and spillage)

Example calculations:

Roof catchment:

  • Building: 185 m² roof
  • Annual rainfall: 762 mm
  • Potential: 185 × 762 = 141,000 liters/year (141 m³)

Hard surface catchment:

  • Parking/driveway: 465 m²
  • Annual rainfall: 762 mm
  • Potential: 465 × 762 = 354,000 liters/year (354 m³)

Passive landscape catchment:

  • Swale catchment area: 0.4 hectares (4,047 m²)
  • Annual rainfall: 762 mm
  • Runoff captured: 4,047 × 762 = 3,084,000 liters/year (3,084 m³)
  • (Note: This infiltrates rather than stores for direct use)

Determine realistic capture percentage:

  • Well-designed system: 75-90% of potential
  • Basic system: 50-75% of potential
  • Account for overflow, losses, and maintenance downtime

Step 3: Design Active Roof Catchment System​

Components needed:

1. Collection surface (roof):

  • Material considerations: Metal best, asphalt shingles acceptable, avoid treated wood
  • Clean surface without debris or contamination
  • Sloped for drainage
  • Area determines potential volume

2. Gutters and downspouts:

  • Sized for peak rainfall intensity
  • Minimum 13 cm (125-130mm) gutters for most applications
  • 75×100 mm downspouts standard
  • Secure installation to handle storm flows
  • Leaf guards to reduce debris

3. First-flush diverter:

  • Diverts initial dirty water (bird droppings, dust, debris)
  • First 38 liters per 93 m² roof discarded
  • Automatic or manual reset
  • Critical for water quality

4. Filtration:

  • Screen filter (200 micron or finer) for debris
  • Optional sand or charcoal filters for higher quality
  • Inline filters before storage
  • Regular cleaning essential

5. Storage (see Build Water Storage Structures):

  • Tanks, cisterns, or ponds
  • Size based on supply and demand analysis
  • Covered to prevent algae, mosquitoes, evaporation
  • Overflow system back to landscape

6. Distribution system:

  • Gravity-fed if possible (elevate tanks)
  • Pump if needed for pressure
  • Drip irrigation or hose bibs
  • Backflow prevention if connecting to any potable system

Design considerations:

  • Place tanks near collection points (minimize piping)
  • Access for maintenance
  • Foundation/pad for stability
  • Freeze protection in cold climates
  • Overflow directed to infiltration areas

Step 4: Design Passive Landscape Harvesting​

Swales (vegetated infiltration trenches):

  • Location: On contour (level along slope)
  • Dimensions:
    • Width: 0.9-3 meters depending on site
    • Depth: 15-45 cm
    • Length: Along contour
    • Berm on downslope side: 15-30 cm high
  • Spacing: Every 6-15 meters of vertical elevation
  • Function: Capture runoff, slow water, allow infiltration
  • Vegetation: Deep-rooted plants enhance infiltration

Berms:

  • Purpose: Direct water to desired locations
  • Height: 15-45 cm
  • Width: 0.6-1.2 meters at base
  • Location: Along contours, around basins
  • Combination: Often paired with swales

Rain gardens/infiltration basins:

  • Size: 10-20% of contributing drainage area
  • Depth: 15-30 cm
  • Location: Low points that naturally collect water
  • Soil: Amended for good drainage if needed
  • Plants: Water-tolerant species that can handle both wet and dry

Terracing:

  • Application: Steep slopes
  • Benefit: Creates level planting areas, slows runoff
  • Construction: Cut and fill to create steps
  • Combination: With berms and swales for maximum effect

Design process:

  1. Map water flow patterns (observe in rain)
  2. Identify high-volume runoff areas
  3. Design systems to intercept before leaving site
  4. Create overflow paths for extreme events
  5. Integrate with planting design

Step 5: Implement Hard Surface Catchment​

Paved areas (driveways, parking, paths):

  • Grade toward: Vegetated areas not storm drains
  • Channel with: Curbs or berms to infiltration basins
  • Break up large areas: Create infiltration pockets
  • Permeable paving: Consider for new construction

Roof runoff from outbuildings:

  • Don't need full cistern systems for every building
  • Direct to rain gardens or swales
  • Rain chains as attractive alternatives to downspouts
  • Splash blocks to prevent erosion

Collection at downspouts:

  • Rain barrels (200-400 liters) for small-scale
  • Daisy-chain multiple barrels
  • Overflow to infiltration areas
  • Mosquito screens essential

Step 6: Install and Test System​

Installation sequence:

For active systems:

  1. Install gutters and downspouts (if not present)
  2. Install first-flush diverter
  3. Install filters
  4. Install storage tanks
  5. Install distribution system
  6. Test all components
  7. Monitor first few rain events

For passive systems:

  1. Mark contours
  2. Excavate swales/berms
  3. Shape basins
  4. Plant vegetation
  5. Test during rain
  6. Adjust as needed

Testing:

  • Test during actual rain events
  • Check for leaks and overflow
  • Verify water quality
  • Adjust as needed
  • Document performance

Step 7: Maintain System​

Regular maintenance:

  • Clean gutters and filters regularly
  • Inspect tanks and connections
  • Check overflow systems
  • Maintain vegetation in swales
  • Monitor water quality
  • Document maintenance activities

💡 Customization Notes​

When using this template for your project:

  1. Climate: Adapt systems to your specific climate and rainfall patterns

  2. Topography: Use your site's topography to your advantage

  3. Budget: Choose system complexity based on available resources

  4. Legal Context: Research and comply with local water regulations

  5. Maintenance: Plan for ongoing maintenance - systems require care

  6. Local Resources: Use local materials, contractors, and expertise

Remember: This is a template. Your actual project will have specific climate, topography, and water needs that make it unique.

Next Steps​

Once rainwater harvesting is implemented: → Task 3: Build Water Storage Structures

Remember: Every drop counts. Rainwater harvesting maximizes the value of precipitation that falls on your site.

This is a template. Customize it for your project.