Rainwater Harvesting Calculator
Free rainwater harvesting calculator. Estimate how much rainwater you can collect from your roof based on catchment area, rainfall, and collection efficiency.
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Calculate Your Rainwater Harvesting Potential
Rainwater harvesting is a sustainable practice that captures and stores rainwater for later use. Our calculator helps you estimate how much water you can collect from your roof based on your local rainfall, roof size, and collection system efficiency.
How Rainwater Collection Works
Every inch of rain falling on a square foot of surface area produces about 0.623 gallons of water. By multiplying your roof area by rainfall and accounting for collection efficiency (losses from evaporation, first flush, and gutter design), you can estimate your harvestable water volume.
Collection Formula
Volume = Area × Rainfall × 0.623 × EfficiencyBenefits of Rainwater Harvesting
Reduce Water Bills
Collected rainwater can be used for irrigation, washing, and with proper treatment, even drinking.
Drought Resilience
Store water during wet periods for use during dry spells or water restrictions.
Environmental Impact
Reduce stormwater runoff and decrease demand on municipal water systems.
How to Calculate Rainwater Collection
Uses for Harvested Rainwater
Garden Irrigation
Plants prefer soft rainwater over chlorinated tap water.
Livestock Watering
Provide clean water for chickens, goats, and other animals.
Emergency Backup
Have water available during power outages or supply disruptions.
Car Washing & Cleaning
Soft rainwater is excellent for outdoor cleaning tasks.
Frequently Asked Questions
Metal roofs can achieve 90-95% efficiency, while asphalt shingles are typically 80-85%. Green roofs may only yield 50% as they absorb significant rainfall.