Rainwater Harvesting Payback Calculator
Estimate annual rainwater collection, usable yield, water-bill savings, net annual benefit and simple system payback.
Default project preview
62.4 years
Annual captured water
32,296 gal
Annual usable water
22,607 gal
Gross annual water savings
$192.16
Net annual benefit
$72.16
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Input and output guide
What each value means
The labels and units below are part of this calculator’s visible methodology. Replace every default with measurements or product data from the actual project.
Collection roof area
Enter this project assumption in ft². The current imperial default is 1800 ft².
Annual rainfall
Enter this project assumption in in/year. The current imperial default is 36 in/year.
Collection efficiency
Enter this project assumption in %. The current imperial default is 80 %. Minimum: 1. Maximum: 100.
Collected water actually used
Enter this project assumption in %. The current imperial default is 70 %. Minimum: 0. Maximum: 100.
Avoided water cost
Enter this project assumption in per 1,000 gal. The current imperial default is 8.5 per 1,000 gal. Minimum: 0.
Installed system cost
Enter this project assumption in a unitless value. The current imperial default is 4500. Minimum: 0.
Annual maintenance cost
Enter this project assumption in a unitless value. The current imperial default is 120. Minimum: 0.
Rebate or incentive
Enter this project assumption in a unitless value. The current imperial default is 0. Minimum: 0.
How to read the outputs
Annual captured water
roof, rainfall and runoff efficiency. Default preview: 32,296 gal.
Annual usable water
70% utilized. Default preview: 22,607 gal.
Gross annual water savings
usable volume × avoided water rate. Default preview: $192.16.
Net annual benefit
gross savings minus maintenance. Default preview: $72.16.
Net upfront cost
installed cost minus incentive. Default preview: $4,500.00.
Collection efficiency
first flush, overflow and system losses. Default preview: 80%.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Captured water = roof area × rainfall × runoff efficiency. Usable water applies the utilization fraction. Net annual benefit = avoided water cost − maintenance. Simple payback = net upfront cost ÷ net annual benefit.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Rainwater Harvesting Payback Calculator questions
Why is usable water lower than captured water?+
Storage overflow, seasonal mismatch and limited non-potable demand can prevent all collected water from being used.
Does the calculator size the storage tank?+
No. It estimates annual yield and economics. Tank sizing needs rainfall timing, demand timing and desired reliability.
What happens when maintenance exceeds savings?+
The calculator reports no positive simple payback because the entered annual net benefit is zero or negative.