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Wastewater Retainage Credit

Procedures and Reporting


  • General
    Any active current industrial, commercial, or institutional user ("User") of the Cobb County Water System is eligible for a credit on wastewater service charges for metered water which is not returned to the sewer system.
  • Procedures and Reporting
    The following paragraphs describe the application procedures for potential participants in the Wastewater Retainage Credit Program and the requirements for periodic reporting of water use and return to the sewer.
    1. The User must retain the services of one of the approved independent engineering firms to develop a location plan for sub-meters, along with a meter-reading schedule, and to prepare the semi-annual Retainage Analyses. The User is required to pay all costs associated with the engineer’s services, the installation and maintenance of sub-meters, and other related work.
    2. Sub-meters shall be installed to measure make-up water, water used in a product, boiler supply water, or other consumptive uses. Also, sub-meters are required on blow-downs, overflows, or product waste streams to measure the return from these sources to the sewer system. The difference in readings between the supply and return sub-meters will reflect the “retained” amount. All meters shall be calibrated annually to maintain accuracy.

    3. The readings of the sub-meters must be recorded by the User on a monthly basis, consistent with the Water System’s meter-reading schedule and billing cycle for the customer. The User may also read and record the Water System meter at the same time the sub-meters are read if desired for coordination of data recording intervals; however, the billing records will govern if there is a discrepancy in readings. If a consistent monthly usage can be demonstrated (after at least two full seasonal periods), the frequency of readings can be reduced to two per season.

    4. All meter readings are compiled and compared to the User’s total water consumption in a Retainage Analysis report that is prepared by the engineering firm. A “Percentage of Water Returned to Sewer” value will be calculated in each Retainage Analysis report and the long-term average will be shown on the Retainage Analysis Summary Form. This percentage will be applied to the User’s wastewater commodity charge in each water bill for a six month period. The long-term average will be recalculated with each subsequent seasonal analysis, using the current period data along with the data for that period from the three previous years of the User’s participation in the program.

    5. The Retainage Analysis, bearing the seal of the preparing professional engineer, is submitted to the Water System twice a year. The report may be in any form deemed suitable by the preparer, as long as it is sufficiently detailed to allow verification of water consumption and return flows.

    6. The seasonal periods, the schedule for submittal, and effective dates for credits follow: 

      Seasonal Period Submittal Due Date* Credit Effective Date
      April 1 – September 1
      October 1 – March 1
      February 1
      August 1
      May 1
      November 1
      * Submittal is due on the first business day following the date indicated.
    7. If it is determined that no significant seasonal variation occurs in the percentage of water returned to the sewer, the Water System may, upon request of the User, elect to waive one of the two annual submittals.
    8. If a new Analysis is not received by the submittal date as required, the User’s credit will be eliminated on the seasonal Effective Date.

Approved Engineers

200 North Cobb Parkway
Bldg 400, Suite 413 
Marietta, GA 30062 
Contact Name: Kelly Knetzger, PE
Phone: (770) 971-5407 
Fax: (770) 971-0620 

100 Arnold Mill Way, Suite A 
Woodstock, GA 30188
Contact Name: Athan P. Tsarouhas 
Phone: (770) 592-1477
Fax: (770) 517-9093

272 Brighton Road
Atlanta, GA  30309
Contact Name: Mike Elmers
Phone: (770) 851-1722

P. O. Box 11586 
Atlanta, GA 30355 
Contact Name: Gray Campbell Thomas OR W. McBroom, Sr, P. E. 
Phone: (404) 355-4445 
Fax: (404) 355-9099 


334 Cherokee Street 
Marietta, GA 30060 
Contact Name: Joe Hartline 
Phone: (770) 427-8123

1205 Johnson Ferry Road, Suite 136-178
Marietta, GA 30068 
Contact Name: Michael DeRosa
Phone: (706) 255-8692
Fax: 706-395-6778

WaterSignal, LLC
510 Staghorn Court
Alpharetta, GA 30004
Contact Name: Aaron Beasley
Phone: (770) 842-4202

1230 Peachtree Street, 300 Promenade 
Atlanta, GA 30309 
Contact Name: John McFarland, P.E. 
Phone: (678) 990-8001 
Fax: (678) 990-5399 


Contact Us

Wilson Collins
Project Engineer
☎ 770-419-6466

Pathenia Freeman
Accounting & Finance Division
☎  770-419-6234 

Cobb County Water System
660 South Cobb Drive 
Marietta, GA 30060


The Cobb County Water System recognizes there are instances where all of the water used by some industrial, commercial, or institutional customers may not be returned to the sewer system for conveyance and subsequent treatment as wastewater. Examples of “retained” water include: evaporative losses in air-conditioning cooling towers, in certain manufacturing processes, or at laundry facilities; water directly used in a product; water supplying a boiler; other similar applications.

Participants in the Wastewater Retainage Credit Program do not have to pay wastewater commodity charges for that portion of metered water which is not returned to the sewer system. A “Retainage Analysis”, prepared twice a year by an approved independent professional engineer employed by the customer, is used to quantify the amount of water “retained” and to establish a long-term average credit percentage value to be applied to the customer’s bill during the six-month seasonal period. Most situations require the installation of sub-meters on specific water-using components to accurately measure the consumption and subsequent return to the sewer.

Wastewater Retainage Credit FAQs

What is a Wastewater Retainage Credit?

This credit is a reduction of the wastewater commodity charge on a customer’s water bill based on the amount of purchased water that is actually returned to the sewer for collection and treatment as wastewater. For example, if a customer can demonstrate that only 75% of the water purchased is returned to the sewer, then the wastewater commodity charge paid is only 75% of the billed water consumption, rather than the standard 100%. The other 25% of the water purchased is “retained” by the customer (e.g., evaporated in a cooling tower, used in a manufactured product, etc.) and is not returned to the sewer.

Are irrigation or landscaping water uses eligible for the program?

No. In order to promote water conservation, these uses are not eligible for the program.  If interested, a customer may purchase an irrigation meter for an irrigation system.  Irrigation accounts are not subject to the wastewater commodity charge, but the irrigation water rate is substantially higher than the commercial water rate.

Are sub-meters always required?

In some rare cases, the Water System has allowed the Retainage Analysis to be based on estimated values; however, in these cases, detailed operating records and other supporting data are necessary to verify the calculated values.

Are the credit values shown separately on the water bill?

No. The credit percentage is applied to the wastewater commodity charge amount during the preparation of the bill, but is not shown as a separate line item.

When do the seasonal credit adjustments become effective?

The "summer" credit is effective on May 1st, while the “winter” credit is effective on November 1st.

Is a formal approval of new participants required?

Not unless the proposed application of the Retainage Program is unusual in nature. The approved engineers are very familiar with the Program, and they can advise prospective participants on the requirements for typical applications and contact the Water System for guidance if warranted.

Are there any service charges imposed by the Water System on customers that participate in this Program?

No. The costs to the customer are related to fees for the engineering firm and for the installation and maintenance of the required sub-meters.

How often should the sub-meters be read?

The sub-meters must be read monthly on the same schedule as the Water System’s reading of the customer’s main meter. If, after at least two full seasonal periods (two of each period), a consistent monthly usage can be demonstrated, the frequency of readings can be reduced to two per season.

Can a customer also read the main meter when the sub-meters are read, to ensure that all data are on a consistent time basis?

Yes; however, if there is a discrepancy in the usage calculations, the Water System’s readings and billing records will govern for the period in question.