Corbelworks · utility & telecom defect scan · worked example

Cooling tower sewer credit: stop paying sewer on water that evaporated

If your commercial property runs a cooling tower, a large share of its makeup water evaporates into the air and never enters the sanitary sewer. Many utilities still bill sewer volume on the full water meter — so you can pay sewer charges on water that physically never reached the drain. This page shows the defect, an illustrative recovery calculation, live utility-program citations you can check yourself, and the exact steps to confirm it on your own bills.

The billing defect, precisely

Most commercial sewer charges are computed as a volume rate applied to your incoming water meter, on the assumption that water in equals wastewater out. A cooling tower breaks that assumption: it rejects heat by evaporating water, and evaporated water does not enter the sewer. Industry references commonly put evaporative loss at roughly three-quarters of tower makeup water, with the remainder leaving as blowdown/bleed-off that does reach the sewer.

When the utility offers an evaporation or "deduct" allowance, the property can install a submeter on tower makeup (or on the blowdown line) and have the evaporated volume credited off the sewer bill. Where the property never applies, it keeps paying sewer on gallons that vanished into the air — a recurring overcharge, not a one-time error.

This is a designed utility mechanism, not a loophole. Utilities publish these allowances specifically so customers are not charged for wastewater service they did not use. The catch is that the credit is opt-in: the property must apply, meter, and document it.

Illustrative recovery calculation

Illustrative only. The numbers below are a fictional worked example to show the method. They are not a customer result, a guarantee, or a promise of savings. Your actual figures depend on your tariff, your metered volumes, and your utility's specific program rules.

Total metered water (annual)	5,000,000 gal
Cooling-tower makeup water (annual)	1,500,000 gal
Assumed evaporative fraction of makeup	~80%
Evaporated volume (never enters sewer)	~1,200,000 gal
Illustrative sewer volume rate	$9.00 per 1,000 gal
Illustrative annual sewer credit	1,200 × $9.00 = $10,800 / year
One-time deduct submeter install (illustrative)	$3,000–$8,000

In this illustration the recurring credit exceeds the one-time metering cost inside the first year, and then compounds every year the tower runs. The decision is therefore an ROI question — annual credit versus metering and application cost — not a guess.

Live program citations you can verify

The point of a worked example is that you can check it. These are real, currently published utility programs — open them and confirm the mechanism before you take anyone's word for it, including ours:

New York City (DEP / NYC Water Board): the Wastewater Allowance for separately metered cooling-tower and similar consumptive uses is defined in the published Water and Wastewater Rate Schedule and applied for through DEP's billing forms. See the NYC DEP billing forms page (Application for Wastewater Allowance — Cooling Towers) and the NYC Water Board FY2025 Rate Schedule.
Fayetteville Public Works Commission (NC): a published Consumptive Water Use and Evaporative Loss Sewer Credit that credits the metered difference (or the full incoming volume where no sewer discharge is anticipated) against sewer charges.
Many other municipalities run equivalent "deduct meter," "sewer submeter," or "evaporation credit" programs (for example Seattle Public Utilities' deduct-meter program for irrigation and cooling-tower makeup). Program names, eligibility, and metering rules vary by jurisdiction, so the operative document is always your utility's tariff or program page.

Because rules differ by utility, the credit is real in one jurisdiction and unavailable in the next. The only way to know your case is to read your applicable tariff against your actual meter configuration — which is exactly what the scan does.

Check it yourself in four steps

On a recent bill, find the sewer volume charge and confirm whether it is computed on your incoming water meter reading.
Estimate cooling-tower makeup for the period (from tower run data, chemical-treatment logs, or a makeup submeter if one exists).
Search your utility's site for wastewater allowance, evaporation credit, deduct meter, or sewer submeter, and read the eligibility and metering requirements.
Compare the annual credit against the one-time submetering and application cost. If credit > cost within a reasonable payback, it is worth filing.

Want this checked against your actual bills?

The Single-Site Utility & Telecom Defect Scan is a fixed-scope, fixed-price ($149) review of three months of one property's utility and telecom invoices. For cooling-tower cases it maps the sewer-volume basis against your metered makeup, checks whether your utility publishes an allowance, and returns a written evidence map, ranked findings, calculation notes, and next steps — including where a required tariff document is still missing. It documents the defect; it does not contact your utility, file the claim, or promise a recovery amount.

Review the $149 fixed-price scan Not ready to pay? Use the no-payment intake

Multiple properties, a portfolio, or a fit/no-fit question first? The no-payment intake gets a scoped next step or an honest decline within 48 hours.