Estimate the treatment cost of rainwater harvesting from flow, variable treatment expense, annual fixed cost, and equipment replacement allowance. The calculator reports annual cost, effective cost per thousand gallons, and a user-defined planning-period total. It is intended for early comparisons between treatment approaches, not a vendor quote or regulatory compliance determination.
Annual cost = annual volume ÷ 1,000 × variable cost + fixed O&M + replacement reserve
The planning-period total multiplies annual cost by years without discounting or escalation.
The main result is estimated annual treatment expenditure at the entered utilization. The effective unit cost spreads both variable and annual fixed costs over treated volume.
Exclude capital purchase price unless it is represented by the replacement reserve. Confirm treatment train, monitoring, labor, residuals disposal, energy, and local requirements separately.
At 500 gal/day for 365 days, annual volume is 182,500 gal. At $2.50/1,000 gal plus $900 fixed cost and $300 reserve, annual cost is 182.5 × $2.50 + $1,200 = $1,656.25.
No. The formula covers entered variable cost, fixed annual operations, and replacement reserve; add capital and plumbing costs separately.
Fixed annual costs are spread over more treated gallons, while the variable cost per thousand gallons stays constant.
Use the variable rate if energy closely follows volume; otherwise include the annual amount in fixed operations.
No. It is a simple undiscounted total with no inflation or escalation.
Yes, but only when that category is genuinely absent or accounted for elsewhere.
| Input concept | Planning use |
|---|---|
| Volume or flow | Use the same gallon basis throughout the calculation. |
| Efficiency or allowance | Enter percentages as displayed, from 0 to 100. |
| Operating condition | Base it on the intended design period, not an unrelated annual peak. |