Most water and sewer utilities bill sewer service on the volume recorded by the incoming water meter, on the assumption that water delivered to a building leaves through its drains. That assumption fails for water that evaporates or soaks into the ground. Cooling towers lose a large share of their makeup water to evaporation and drift; only the blowdown goes to the drain. Irrigation, evaporative condensers at refrigerated warehouses, process water that leaves in product and boiler makeup all follow the same pattern. Many municipal utilities allow a sewer deduction when this water is measured by a separate deduct meter, sometimes called a submeter or sewer credit meter, installed on the line feeding the tower or irrigation system. The rules vary by city: the meter may need to meet a specification, be approved and inspected, and be read by the utility or reported by the customer on a schedule. Sites often have the meter but never registered it, stopped reporting reads, or lost the credit in a billing system change.
How it happens
- A deduct meter was installed on the cooling tower makeup line but never registered with the utility.
- The customer stopped submitting deduct meter reads, so credits stopped.
- The utility applies the deduction to water but not to sewer, or to sewer but not to stormwater or volume-based fees that follow sewer.
- Irrigation shares a meter with the building and no separate irrigation meter or deduct meter was ever installed.
- A billing system migration dropped the deduct account link.
How to detect it
- List every site with a cooling tower, evaporative condenser or irrigation and check whether its sewer volume is lower than its water volume.
- Read the city or utility's sewer credit rules: eligible uses, meter specs, approval and reporting requirements.
- Compare deduct meter reads (or tower makeup estimates from conductivity and cycles of concentration) to credits shown on bills.
- Note units: water bills commonly use CCF (hundred cubic feet, about 748 gallons) or thousands of gallons.
Evidence the utility will accept
- Deduct meter installation records, make, model and test certificate
- The utility's approval or registration of the deduct meter, if required
- Logged deduct meter reads for the claim period
- Water and sewer bills showing metered volume and sewer volume
Recovering the overcharge
We submit the logged deduct meter reads and approval documents to the utility and request a sewer credit for each period, then set up the reporting schedule so credits continue. Look-back periods for sewer credits are set by local ordinance or utility policy and are often shorter than for electric billing errors, sometimes limited to the current or prior year, so prompt filing matters. Where no deduct meter exists, we size the savings to justify installing one.