C
Calcuable

Rainwater Harvesting

Water harvesting potential.

m²
mm

Explanation

Harvesting rainwater is eco-friendly and saves money. This calculator estimates the harvestable volume based on roof area and rainfall. ### Formula **Volume = Roof Footprint Area x Rainfall x Efficiency**. - **Area**: The footprint of the roof (pitch doesn't increase rain catch!). - **Rainfall**: Annual average in inches or mm. - **Efficiency**: 0.90 for metal/tiles, 0.80 for flat/gravel. ### Rule of Thumb - 1 inch of rain on 1,000 sq ft roof = approx 600 Gallons. - (Area sq ft x Rainfall inches) / 1.6 = Gallons (approx). ### Tank Sizing Usually size for 2-4 weeks of dry spell supply.

Examples

  • Roof 1000 sq ft. Annual rain 30 inches.
  • Total Harvest = 1000 x 30 x 0.623 (conversion) x 0.9 = ~16,800 Gallons/year.
  • A 50-gallon barrel fills up in minutes during a storm!

FAQ

Is it potable?

No, roof runoff contains bird droppings and pollutants. Use for garden/flushing only unless heavily treated.

First flush?

A first-flush diverter is recommended to discard the first few gallons of dirty wash-off.

Disclaimer

Results are for reference only and do not replace professional advice.