How Much Can My Building Save with Sewer Credits?

Quick Answer

Most commercial buildings with cooling towers save 15 to 30 percent of their sewer charges through sewer credits, with the full range across building types running from 10 percent (retail with rooftop units) to 40 percent (campuses with central plants). In dollars, a mid-size building paying $4,000 per month in sewer charges typically recovers $12,000 or more per year, while large campuses can exceed $100,000 annually. You can estimate your own number in minutes: multiply your monthly sewer charge by the percentage of purchased water that never reaches the sewer — for most buildings with cooling towers, that’s 15 to 35 percent. Actual credits are set by metered data, so treat the estimate as a screening tool, not a final answer.

It’s the first question every facility manager asks: how much money are we actually talking about? The answer depends on your building type, cooling system size, and local sewer rates — but the math is surprisingly simple, and you can get a rough estimate in about two minutes.

The Quick Estimation Formula

Here’s the back-of-the-envelope calculation: take your monthly sewer charge and multiply it by the estimated percentage of your water that doesn’t reach the sewer system. That percentage is your savings potential.

Monthly Savings = Monthly Sewer Charge × Non-Sewer Water Percentage

For example, if your monthly sewer bill is $5,000 and your cooling tower evaporates roughly 25 percent of your total water use, your potential savings are approximately $1,250 per month — or $15,000 per year. It’s not exact (actual credits are based on metered data, not estimates), but it gives you a reliable order of magnitude to work with.

Typical Savings by Building Type

The non-sewer water percentage varies significantly by building type because different facilities have different water use profiles. Based on industry data and our experience working with commercial clients, here are typical savings ranges:

Office buildings with cooling towers typically save 15 to 30 percent on sewer charges. Cooling towers are usually the only significant non-sewer water use, but they can be substantial. A 500-ton tower serving a large office complex might evaporate 80,000 to 120,000 gallons per month during summer. The Department of Energy estimates that evaporation accounts for the majority of cooling tower water consumption.

Hotels and hospitality save 20 to 35 percent because they have multiple non-sewer water uses: cooling tower evaporation, pool evaporation and backwash, laundry water losses, and landscape irrigation. These sources stack to create a larger total credit.

Universities and campus facilities often save 25 to 40 percent. Large campuses may have multiple cooling towers, central boiler plants with steam losses, extensive irrigation systems, and laboratory process water — all of which qualify for credits in most jurisdictions.

Retail centers and malls typically save 10 to 25 percent. Savings depend heavily on whether the property has a central plant with cooling towers versus individual rooftop units (which generally don’t qualify for significant credits).

Real Dollar Amounts

To put percentages into dollars, consider that commercial sewer rates in major U.S. cities range from $6 to $15 per thousand gallons, according to EPA water rate data. A mid-size commercial building using 400,000 gallons per month at $10 per thousand gallons pays $4,000 monthly in sewer charges. A 25 percent credit saves $1,000 per month, or $12,000 per year.

Larger facilities see proportionally larger savings. A university campus with multiple towers and $25,000 in monthly sewer charges saving 35 percent recovers $8,750 per month — over $100,000 per year. Our ROI case studies document real facilities achieving savings in these ranges.

The Variables That Move Your Number

Two buildings with identical cooling towers can receive very different credits, and the differences usually come down to four variables. The first is your local sewer rate — a credit on 100,000 gallons is worth $600 per month at $6 per thousand gallons and $1,500 at $15. The second is cycles of concentration, the ratio of dissolved minerals in your tower water compared to fresh makeup water. At 3 cycles of concentration, roughly two-thirds of your makeup water evaporates and one-third goes to the sewer as blowdown. At 6 cycles, about 83 percent evaporates. Better water treatment supports higher cycles, which means a larger share of your water qualifies for the credit.

The third variable is operating hours — a tower serving a data center runs year-round, while an office tower in a temperate climate may run hard only five months a year. The fourth is your utility’s program design: some credit 100 percent of documented evaporation, while others apply caps, minimum thresholds, or processing fees that trim the net savings. Ask for the program rules in writing before you build your business case.

How Seasons Change the Math

Evaporation is not flat across the year. A cooling tower in a four-season climate can evaporate two to three times more water in July than in January, because evaporation tracks heat load and weather. Your credit is naturally larger in summer months and smaller in winter — which is exactly why utilities typically require 60 to 90 days of baseline data, and sometimes a full cooling season, before approving a credit.

When you budget, use annual figures rather than extrapolating from a single month. A January meter reading will understate your credit; an August reading will overstate it. For a quick sanity check before metering, pull 12 months of water bills and look at the summer-to-winter spread in total consumption. For buildings without irrigation, most of that seasonal swing is cooling tower load — a rough but useful proxy for the evaporation your meters will eventually document.

Why Estimates Are Just the Beginning

The formula above gives you a starting point, but actual savings are determined by metered data — not estimates. Your cooling tower’s evaporation rate depends on weather, operating hours, cycles of concentration, and equipment condition. The only way to know your exact savings potential is to install meters and measure. That said, the estimate tells you whether the savings justify the investment in metering — and for virtually any building with a cooling tower over 200 tons, the answer is yes.

For a detailed breakdown of what submetering costs and how quickly it pays for itself, see our water monitoring ROI analysis.

Want to see whether your building qualifies? Learn how RPM recovers evaporation and sewer credits for commercial facilities.

Don’t Guess — Measure

Your estimate gives you a reason to act. Metered data gives you the exact number. RPM’s free assessment can tell you precisely what your building would save based on your specific equipment, water use, and local sewer rates — no guessing required.