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Planning Tool

Rainwater Collection Planner

Estimate how much rainwater a roof could potentially collect from a given rainfall amount before planning storage or treatment.

Build your collection estimate

Use simple early-stage assumptions. The result represents potential collection, not a guaranteed water supply.

How the estimate works

One inch of rain falling on one square foot of catchment represents approximately 0.623 gallons of water. The planner applies that conversion to your roof area and rainfall, then applies the selected collection-efficiency assumption.

0.623 galPer sq ft per inch of rain
80%Default collection efficiency
PotentialNot guaranteed supply
Important: This planner estimates potential rainwater collection volume only. It does not determine potable-water safety, treatment requirements, first-flush design, tank sizing, overflow management, roof-material suitability, local code compliance, or whether rainfall is sufficient to meet long-term demand. Verify final system requirements with applicable local authorities and qualified professionals.

From collection to storage

Once you have an estimated collection volume, compare it with your planned storage capacity and expected water demand. Water Storage Planner → can help establish a separate early-stage storage target.