Rainwater event capture

MEASURE FIRST

How to prepare your inputs

Use measured catchment, internal pipe dimensions, actual flow or specified gradients. Keep rainfall depth, flow rate and stored volume distinct.

How this calculation works

Gross runoff L = horizontal catchment m² × rainfall mm. Collected runoff = max(0, gross × efficiency − first flush). Stored water is limited by available space.

Assumptions & exclusions

One-event scenario only. Efficiency and first flush are entered assumptions, not design recommendations. Does not predict annual supply, tank sizing, water quality or drainage capacity.

Your next step

Discuss plumbing connections, drainage capacity, water quality and the required design with a licensed plumber.

Further reading

• YourHome rainwater guidance

These resources provide background information. Confirm current product specifications and project requirements with your supplier or trade professional.

What if my shape or product is different?

Use dimensions and product data that match the stated method. For complex work, calculate separate sections or obtain a project-specific take-off. Do not apply simple geometry to structural or compliance decisions.

Why are quantities rounded up?

Whole bags, packs, sheets or cartridges round up to purchasable units. Decimal area or volume results are planning figures; confirm order increments with the supplier.

Are my entries saved?

No. Entries remain in the current browser page and clear on reload. Printing can save your results and inputs as a PDF on your device.