What this tool does
Expose overflow, unmet demand, empty periods and end storage that an annual yield total cannot show.
When to use it
Use for comparative preliminary tank scenarios. Enter local monthly rainfall and test dry, typical and wet years; use daily historic rainfall for detailed design.
Inputs and supported units
Each labelled field explains the quantity it expects. Unit-system changes convert existing numeric entries once and keep calculations on a single SI internal basis. Supported shared units include L/min and GPM, metres and feet, kPa and psi, millimetres and inches, kW and hp, and °C and °F as relevant.
Calculation or decision method
Reliability is the fraction of 365 days on which the complete entered daily demand is supplied.
How to interpret the result
Read the primary result with the supporting breakdown and warning. A plausible number is not evidence that every input, operating case or design constraint has been included.
Worked example
A 10,000 L tank, 150 m² roof, 80% collection factor and 250 L/day demand can be compared across multiple monthly rainfall sequences; the monthly report identifies overflow and unmet demand.
Assumptions
Each month’s rain falls evenly across its days; demand is constant; one non-leap year is modeled; collection factor already includes runoff and system efficiency.
Limitations
Even rainfall distribution smooths storms and dry spells and can overstate reliability. No water-quality, pump, treatment or demand-timing model is included.
Sources
- U.S. Department of Energy — Rainwater Harvesting Tool Help Guide
- Australian Government — YourHome Rainwater Guidance
- U.S. CDC — Collecting Rainwater and Your Health