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Desalination Water Savings Estimator

The Desalination Water Savings Estimator calculates how much conventional freshwater supply can be displaced by desalinated product water over a year. It limits the daily offset to the lesser of eligible demand and available desalinated water, then multiplies by operating days and estimates avoided purchase cost from a user-entered water rate.

The tool is useful for comparing supply portfolios, especially where desalination is intended to reduce dependence on imported, trucked, or otherwise constrained freshwater. The annual water-savings result represents substituted source water, not net environmental benefit. Desalination still has energy, intake, concentrate-management, and treatment requirements that should be evaluated separately. The cost-avoidance value likewise reflects only the entered avoided water rate and should not be read as net project savings.

Imported-water offset

gal/day
gal/day
days/yr
$/1k gal
Result
—
Annual freshwater offset
Daily source-water offset—
Avoided supply cost—
Demand supplied—

1. Enter eligible freshwater demand
Use only demand that desalinated water can actually serve.

2. Enter available desalinated water
Provide the expected product-water supply available to displace that demand.

3. Set annual operating days
Reflect planned production and demand availability over the year.

4. Add the avoided supply rate
Use the cost per 1,000 gallons of the freshwater source being displaced.

5. Review annual offset
Compare gallons displaced, daily offset, demand coverage, and gross avoided supply cost.

Annual freshwater offset = min(Eligible demand, Desalinated water available) × Operating days

Where:

  • Eligible demand: freshwater demand in gallons per day
  • Desalinated water available: usable product water in gallons per day
  • Operating days: days per year when substitution occurs
  • Avoided supply cost: annual offset ÷ 1,000 × avoided supply rate

Assumption: The model treats product water as a direct substitute for the eligible source. It does not subtract feed-water withdrawals, process losses, or desalination operating cost from the water-offset result.

What the result means

The main result is a planning estimate derived directly from the entered operating assumptions and should be interpreted within the stated system boundary.

Use project-specific design criteria, equipment data, and applicable requirements before making final engineering or procurement decisions.

Given:

  • Eligible freshwater demand = 180,000 gal/day
  • Desalinated water available = 150,000 gal/day
  • Operating days = 350
  • Avoided supply rate = $9.25/1,000 gal

Calculation:
Daily offset = min(180,000, 150,000) = 150,000 gal/day.
Annual offset = 150,000 × 350 = 52,500,000 gal.
Avoided supply cost = 52,500 × $9.25 = $485,625.

Result:
52,500,000 gallons per year, with $485,625 of gross avoided supply cost.

Available desalinated water covers about 83.3% of the eligible daily freshwater demand on operating days.

Does freshwater offset equal net water savings for the whole desalination system?

No. The result measures demand displaced at the point of use. Feed-water intake and concentrate generation are separate water-balance quantities.

What demand should be considered eligible?

Use demand that can receive desalinated product water at the required quality and pressure. Exclude uses that cannot be served by the modeled supply.

Can the avoided supply rate include delivery charges?

Yes, if those charges truly disappear when the conventional supply volume is displaced. Keep the rate consistent with the cost question you want the result to answer.

How should plant outages be reflected?

Reduce operating days or available daily volume to represent planned and expected downtime. A detailed monthly model may be better when outages are highly seasonal.

How is this different from a desalination cost estimator?

Water savings measures substituted supply volume; the treatment-cost estimator measures the expense of producing the desalinated water.