Rainwater Collection

Rainwater harvesting is one of the most effective ways to secure an independent water supply. A properly designed system can provide significant amounts of clean water for drinking, sanitation and gardening. This guide presents practical rainwater collection methods.

1. Collection system basics

An effective rainwater collection system consists of several key elements: collection surface, gutters, filters, storage tank, and distribution system.

Key information

Every 25mm of rain on 100m² of roof yields approximately 2,500 liters of water. Even in drier regions, rainwater harvesting can significantly supplement your water supply.

Independence: Reduces reliance on municipal water supply
Water quality: Rainwater is naturally soft and free of chlorine
Cost savings: After initial investment, water is essentially free

Important warning

Rainwater from roofs must be filtered and treated before drinking. Roofs may contain bird droppings, dust, leaves and other contaminants.

2. Collection surfaces

The roof is the main collection surface for most systems. The type of roofing material affects both the quantity and quality of collected water.

Key information

Metal and tile roofs are best for drinking water collection. Avoid asphalt and tar roofs as they release harmful chemicals.

Best materials:

• Metal sheet (galvanized, aluminum, stainless steel)
• Clay or concrete tiles
• Slate

Materials to avoid:

• Asphalt shingles (contains petroleum compounds)
• Tar paper roofing
• Lead flashings or paint containing lead

3. Gutters and transport system

Gutters and downspouts transport water from the roof to the storage tank. Their proper sizing and installation is crucial for system efficiency.

Key information

Use aluminum, stainless steel, or food-grade PVC gutters. Avoid galvanized steel in the first years as it may leach zinc.

Sizing: Minimum 125mm wide gutters for standard roofs
Slope: 2-3mm drop per meter for proper water flow
Maintenance: Clean gutters at least twice a year

Important warning

Install mesh guards on gutters to prevent leaves and debris from entering the system. This significantly reduces maintenance and improves water quality.

4. First flush and filtration

The first rain after a dry period washes accumulated dirt from the roof. A first flush diverter removes this contaminated water automatically.

Key information

A first flush diverter should remove approximately 1 liter per 1m² of roof area. This significantly improves stored water quality.

Filtration stages:

1. Pre-filter: Mesh screen at gutter - removes leaves and large debris
2. First flush: Diverts initial contaminated runoff
3. Sediment filter: Removes fine particles before storage
4. Post-storage: UV or carbon filter before consumption

5. Storage tanks

Proper storage is essential for maintaining water quality. Tank material, location, and sizing all affect the system's effectiveness.

Key information

Choose food-grade tanks specifically designed for water storage. Dark colors prevent algae growth by blocking light.

Tank types:

• Polyethylene (HDPE): Affordable, lightweight, UV-resistant
• Fiberglass: Durable, doesn't affect taste, more expensive
• Concrete/Ferrocement: Long-lasting, naturally alkaline (neutralizes acidic rainwater)
• Stainless steel: Premium option, extremely durable

Calculate tank size based on: average rainfall, roof area, dry season length, and daily water needs.

6. Treatment for drinking

While rainwater is relatively clean, it requires treatment before drinking to ensure safety from bacteria, viruses, and other contaminants.

Key information

Combine multiple treatment methods for best results: filtration + UV or chlorination provides comprehensive protection.

Recommended treatment methods:

1. Sediment filter (5 micron) - removes particles
2. Carbon filter - removes odors and improves taste
3. UV sterilizer - kills bacteria and viruses
4. Optional: chlorination for residual disinfection

Summary

A well-designed rainwater harvesting system provides valuable water security and independence. Regular maintenance and proper treatment ensure safe, clean water for all household needs.