Rainwater Harvesting Calculator 2026

Calculation Result

Your estimated rainwater collection is 2400 liters annually. This calculation is based on a roof area of 120 m², an average rainfall of 25 mm per year, and a collection efficiency of 80%.

This means you can significantly reduce your dependency on mains water and promote sustainable practices in your household.

How the Calculator Works

The rainwater harvesting calculator uses a simple formula to estimate the amount of rainwater you can harvest. It multiplies your roof area by the amount of rainfall to get the total water available. Then, it considers the efficiency of your collection system to provide a realistic estimate of how much water you can actually store and use.

Example Calculation

Let's say you have a roof area of 150 m², an average rainfall of 30 mm, and a collection efficiency of 75%. The calculation would be:

• Total Rainwater = Roof Area (m²) × Rainfall (mm) = 150 × 30 = 4500 liters
• Effective Collection = Total Rainwater × Efficiency = 4500 × 0.75 = 3375 liters

Thus, you would collect approximately 3375 liters of rainwater annually.

Extra Tips

To maximize your rainwater harvesting, consider installing a first flush diverter to remove contaminants from the initial rainfall. Additionally, ensure your storage tanks are covered to prevent evaporation and contamination. Regularly check and clean your gutters to maintain good flow and efficiency.