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Wastewater Treatment Water Savings Estimator

This estimator calculates annual potable-water savings from reusing treated wastewater. It multiplies the available reuse flow by the number of operating days and the percentage of that flow that actually replaces potable or other fresh-water demand. The tool is useful for facilities evaluating reuse for irrigation, cooling, washdown, process makeup, or other applications where reclaimed water can offset a higher-quality supply.

The offset percentage matters because not every gallon of treated effluent necessarily displaces a gallon of potable water. Demand may be seasonal, reuse systems may be offline, or only part of the treated flow may meet the receiving use. The result estimates volume savings only; it does not test water-quality suitability, calculate treatment costs, or determine regulatory eligibility for a reuse application. Use a realistic operating schedule and a defensible offset fraction for planning.

Calculator inputs

gal/day
days/yr
%
Result
—
Estimated annual potable water savings
Gross reusable volume—
Effective daily offset—
Unused / non-offset share—

1. Enter reusable treated flow
Use the amount of treated wastewater expected to be available for reuse on an operating day.

2. Set annual operating days
Enter the number of days per year the reuse application is expected to operate.

3. Estimate potable offset
Enter the percentage of reusable flow that will truly replace potable or other fresh-water demand.

4. Review gross and effective savings
The main result shows annual potable-water savings. The breakdown distinguishes total reusable volume from the portion that does not offset fresh water.

Gross reusable volume = Reuse flow × Operating days
Annual water savings = Gross reusable volume × Potable offset ÷ 100

Reuse flow is entered in gallons per day and operating time in days per year. The potable-offset percentage is limited to 0–100% because it represents the share of reuse that replaces an existing fresh-water demand.

This formula assumes daily reuse flow is reasonably represented by the entered value on operating days. Seasonal or highly variable systems can be modeled in separate periods and summed.

What the result means

The result is the annual volume of potable or fresh water displaced by the modeled wastewater reuse program.

A reuse project may have additional benefits or constraints related to discharge reduction, water quality, storage, energy, and permits that are not represented here.

Given: 75,000 gal/day available for reuse, 280 operating days, and 70% potable offset.

Calculation: Gross reuse = 75,000 × 280 = 21,000,000 gal/yr. Savings = 21,000,000 × 0.70 = 14,700,000 gal/yr.

Result: The reuse program offsets about 14.7 million gallons per year of potable water.

Why might potable offset be less than 100%?

Reuse supply can exceed demand, operate at different times, or replace a non-potable source rather than potable water. The percentage lets you model only the portion that creates a true fresh-water offset.

Should operating days include maintenance shutdowns?

No. Use the days when the reuse application is expected to receive water. Excluding planned downtime generally gives a more realistic annual volume.

Can I model seasonal irrigation reuse?

Yes. You can enter only the irrigation season days, or run separate seasonal cases if the daily flow changes significantly.

Does the calculator confirm reclaimed water is allowed for my use?

No. Water-quality requirements and permitted reuse applications vary by jurisdiction and site. Confirm those separately before implementation.

How is this different from wastewater recovery rate?

Water savings measures potable demand displaced. Recovery rate measures the percentage of wastewater influent converted into recovered effluent, regardless of whether that effluent replaces potable water.