toolbox
Home / Energy & Sustainability / Rainwater Harvesting Recovery Rate Estimator

Rainwater Harvesting Recovery Rate Estimator

This estimator measures how much of the rainwater reaching the collection system becomes usable recovered water after diversion, treatment, overflow, and other losses. It expresses system performance as a recovery percentage and also shows the unrecovered volume. The metric is useful for comparing operating periods, assessing changes after maintenance, or checking how much captured rainwater is actually available for end use. Enter the gross inflow to the harvesting system and the usable volume delivered from the system over the same period. Because the result is volume-based, both values must use the same unit. A high recovery rate does not by itself indicate water quality, adequate storage, or overall water savings.

Inputs

L
L
Result
—
Rainwater recovery rate
Usable recovered water—
Unrecovered volume—
Loss rate—

1. Enter collected volume
Use the gross rainwater volume entering the system boundary for the selected period.

2. Enter usable volume
Enter the water that remains available for the intended use after system losses.

3. Use matching units
Both values can be liters, gallons, or another volume unit as long as they are identical.

4. Use the same period
Compare volumes from the same storm, month, season, or year.

5. Review recovery and losses
Use both the recovery rate and unrecovered volume to understand system performance.

Recovery rate (%) = Usable recovered volume ÷ Collected volume × 100 Unrecovered volume = Collected volume − Usable recovered volume Loss rate (%) = 100 − Recovery rate

The usable volume should not exceed the collected volume for the same system boundary and period.

What the result means

The recovery rate is the share of collected rainwater that remains usable after losses within the defined system boundary.

Define the system boundary consistently when comparing periods; changing whether first-flush, overflow, or treatment reject is included can change the reported rate.

Given
Collected volume = 10,000 L; usable recovered volume = 8,200 L.

Calculation
Recovery rate = 8,200 ÷ 10,000 × 100 = 82%.
Unrecovered volume = 10,000 − 8,200 = 1,800 L.
Loss rate = 18%.

Result
82.0%

The system retains 82% of collected rainwater as usable water under the selected measurement boundary.

What counts as recovered water?

Use the volume that is actually available for the intended end use after the losses you have chosen to include in the system boundary.

Why can recovery be lower after heavy rain?

A full tank may overflow during large events, so more collected water can be lost even though total rainfall is higher.

Can the recovery rate exceed 100%?

Not for a consistent single-source volume balance. If usable volume exceeds collected volume, check meter periods, unit conversions, or whether another water source entered the system.

Is recovery rate the same as collection efficiency?

No. Collection efficiency usually describes the share of rainfall that reaches storage. Recovery rate describes the share of collected water that remains usable after downstream losses.

Does a high recovery rate mean high water savings?

Not necessarily. Savings also depend on rainfall supply, eligible demand, storage, and whether recovered water displaces another water source.