Potencial captação chuva
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
A × P × 0.8
About this calculator
The Rainwater Harvesting Potential calculator estimates the volume of rainwater that can be collected from a surface (e.g., a roof) in a year. The formula used is Volume = Area (A) × Annual Precipitation (P) × 0.8, where 0.8 represents the system's typical efficiency (accounting for losses from evaporation or runoff).
Area (A) must be measured in m² (e.g., 50 m² for a 50 m² roof). Precipitation (P) is the local annual rainfall in liters per square meter (e.g., 1,200 L/m² in an area with 1,200 mm/year). The result indicates the theoretical storage capacity for rainwater collection systems.
Use this tool when planning cisterns, reservoirs, or rainwater reuse systems. Consider additional factors like inflow rate, family demand, and annual climate fluctuations.
Important: The calculation assumes ideal conditions. In practice, efficiency may vary between 70% and 90%, depending on roof slope, roofing type, and collector maintenance. Always consult a specialist for large-scale projects.
Frequently asked questions
Why multiply by the efficiency factor 0.8?
The 0.8 factor accounts for common losses in collection systems, such as evaporation, soil infiltration, or pipe leakage. Higher values (up to 0.9) may apply to well-maintained roofs.
Is the area measured only from the roof?
Yes, typically. Sloped roofs are most efficient. Flat surfaces (e.g., courtyards) may have lower efficiency due to reduced direct runoff.
How to find annual precipitation for my location?
Consult data from ANA (Brazil's water agency) or local meteorological stations. Sites like INMET provide historical averages by region.
Can I use this calculator in areas with prolonged droughts?
Yes, but use 10-year averages for realistic results. In regions with seasonal variations, the output might underestimate dry periods.