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Water Loss

Reference Number: MTAS-1388
Reviewed Date: 03/28/2023

Water Loss and Infiltration/Inflow
Two areas of concern for water and sewer systems are control of water loss from the water system and infiltration/inflow (I & I) into the sewer system. Water loss can be measured in terms of accounted for losses and unaccounted for losses. Water loss comparisons are made by looking at the reports of actual water treated and pumped into the system by the water plant and comparing them with gallons billed and sold to customers. It is important to understand that every thousand gallons treated and pumped at the water plant costs the water system in labor, chemicals, pumping charges, etc. A certain amount of unmetered water is going to pass through the system each month. Some of that water loss can be identified and accounted for. These accounted for losses are the result of:

  • washing filters at the water plant;
  • water from fire hydrants used in firefighting;
  • tank maintenance; and
  • water used in flushing of water lines (especially important to flush dead-end lines).


At the March 24, 2022, meeting of the Water and Wastewater Financing Board (“WWFB”) and at the April 28, 2022 meeting of the Utility Management Review Board (“UMRB”), the Boards decided to overturn the October 7, 2010, decision and June 6, 2012, reaffirmation to adopt the American Water Works Association (AWWA) water loss methodology for water loss referrals. All WWFB and UMRB entities should now submit their water loss information using the Utility Annual Information Report as provided by the Comptroller of the Treasury. The water loss methodology can be obtained from the state comptroller's office.

At the above referenced March 24 and April 28, 2022 meetings, the following was adopted by the Boards:

I. Require that the Utility Annual Information Report contain fields relative to water loss standards regarding the volume of water loss. It is the intention of the Board that the AWWA water loss tool will be required for completion by a third party upon a water loss referral being generated. The Water Loss Form is not considered audited information and is not required to be submitted simultaneously with the audit.

II. In accordance with TCA 68-221-1010(d)(1) and TCA 7-82-401(h)(1) as amended through 2022 Public Chapter 657, failure to include the required schedule constitutes excessive water loss and referral to the appropriate board.

THEREFORE, failure to submit the proper water loss form as decided by the board to be received by the Comptroller of the Treasury will result in the System being referred to the appropriate Board.

III. Further, utilities will be referred to the Board(s) based on:

A. Based on water loss by volume greater than 40%.

Failure to achieve the designated levels will result in a referral to the Board(s)

The requirements will be reviewed by the Boards annually to ensure the desired results are being achieved. The basis for referral is subject to change by approval of the Board(s).

Infiltration/inflow (I & I) occurs when outside ground water enters the sewer system. I & I can cost utilities tremendous amounts of money in pumping and treatment costs. Ground water can enter the sewer system in several different ways:

  • Through cracks or breaks in the sewer lines;
  • Through manholes that are either leaking or located in a low lying area that is prone to being underwater; and
  • Through storm water drains or downspouts that are connected to the sewer system.

Many sewer systems are built with pumping stations that pump to the treatment plant. Obviously, if a lot of outside ground water is entering the system, it must be pumped as well. The resulting additional pumping costs are lost dollars as no customer is being billed for the I & I. Once the I & I reaches the plant the treatment costs rise as well through additional labor costs, chemicals, pumping, etc., which are necessary to treat the waste. In a very rainy season, I & I will amount to thousands of dollars each month. In very bad I & I situations the sewer plant may be operating at capacity because of the excess water, and plant expansions costing thousands, or even millions, of dollars have to be made.

Utilities can do several things to help eliminate I & I. Manholes located in low lying areas need to be either raised or moved. Utility employees can inspect manholes when it is raining to see if outside ground water is entering. Leaking manholes can be replaced or repaired. Many sewer utilities use cameras that can be put through sewer lines to check for leakage. These camera units can be bought (perhaps cities located near each other could agree to purchase and share a camera) or rented. There also are companies that cities can contract with to film their lines. Once identified, a priority list can be established for the orderly replacement of the leaking lines. Through the use of smoke testing, utilities can find storm drains and downspouts that are connected to the sewer system. Property owners can be notified to remove the drains and downspouts from the system. Those who refuse may be cited under the city’s sewer use ordinances.