Sewer charges on water that never reached the sewer
Cooling towers and irrigation consume water that never enters the sanitary sewer. How sewer billing works and how deduct and irrigation meters correct it.
Sneha Patil · March 17, 2026 · 6 min read
Key takeaways
- Sewer charges are usually computed from metered water use, on the assumption that most of it returns to the sewer.
- Cooling tower evaporation and landscape irrigation are consumed or absorbed, so billing sewer on them overcharges.
- Relief generally requires a separate meter (a deduct or irrigation meter) or an approved allowance, and the rules differ by municipality.
How sewer charges are usually built
Most municipal and regional systems do not meter wastewater leaving a commercial property. They meter the water coming in and bill sewer on a function of it, often the full volume or a percentage, sometimes capped by winter averaging for residential-style accounts. The assumption is simple: nearly all the water a building uses ends up going down a drain.
The assumption is wrong for specific uses. Where water is evaporated, absorbed into a product, or applied to the ground, it does not enter the sewer, and an account billed sewer on every gallon that passes the water meter pays for treatment that never happened.
Cooling towers and evaporative equipment
A cooling tower rejects heat by evaporating water. The make-up water that replaces it is metered as ordinary water use. A large share of that make-up evaporates and leaves as vapor. Only the blowdown, the water bled off to control dissolved solids, goes to the drain. In a typical tower the evaporated portion is substantially larger than the blowdown, though the exact split depends on the cycles of concentration the system is run at.
Evaporative condensers on refrigeration plants, process cooling and some humidification systems behave similarly. For industrial cold storage and food processing sites, the volume involved can be a large part of the water bill, and the sewer charge on it can match or exceed the water charge itself.
Irrigation and other consumed water
Landscape irrigation is the other common case. Water applied to turf and plantings does not return to the sanitary sewer. Many utilities permit or require irrigation to be served through a separate meter, which is billed for water only. A site that irrigates through the building's domestic meter is billed sewer on it by default.
Water incorporated into a product, such as beverage or food manufacturing, is a third case. It leaves the site in the product. These situations are less standardized, and the available relief varies widely by municipality.
What relief looks like
The usual mechanism is a deduct meter, a second meter on the make-up line or the irrigation line that measures the volume to be excluded from the sewer billing basis. Some municipalities offer an approved percentage allowance instead, or a sewer exemption for irrigation. Installation requirements, approved meter types, inspection and application forms are set by the water or sewer authority.
Whether relief can be retroactive is a policy question that differs by authority. Many give credit from the date of approval or installation, and some will credit earlier periods when a prior over-billing can be documented. Ask before assuming either way.
Finding it in a portfolio
The signal is a site whose water and sewer volumes are identical on every bill, combined with equipment or landscape that obviously consumes water. A distribution center with a cooling tower or a large landscaped campus billed sewer at 100% of metered water use is a candidate.
The work is to document the equipment, confirm the municipality's rules, and apply for a deduct or irrigation arrangement. Where the installation is cheap relative to the annual overcharge, payback is often under a year.