Water Loss and Infiltration/Inflow

Two major operational concerns for water and sewer systems are water loss in the water system and infiltration/inflow (I&I) into the sewer system.

Water Loss

Water loss is measured as accounted-for and unaccounted-for losses. Comparisons are made by evaluating the volume of water treated and pumped at the water plant against the volume billed and sold to customers. Every thousand gallons of treated and pumped water incurs costs in labor, chemicals, and energy, so minimizing losses is important for both efficiency and cost control.

Some unmetered water loss is expected and can be accounted for. Common causes of accounted-for losses include:

• Washing filters at the water plant
• Water used for firefighting through fire hydrants
• Tank maintenance
• Flushing of water lines, particularly in dead-end lines

Regulatory Requirements

At the March 24 and April 28, 2022 meetings, the following was adopted regarding water loss reporting:

1. Utility Annual Information Report:
   • Must include fields related to water loss volume standards.
   • The AWWA Water Loss Tool is required for completion by a third party when a water loss referral is generated.
   • The Water Loss Form is not considered audited information and does not need to be submitted with the audit.
2. Legal Reference:
   • 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 results in referral to the appropriate board.
3. Referral Thresholds:
   • Utilities with water loss volumes greater than 40% will be referred to the Board(s).
   • Referral criteria are reviewed annually by the Board(s) and may be adjusted to meet desired outcomes.

Infiltration and Inflow (I&I)

Infiltration/Inflow occurs when outside groundwater or stormwater enters the sewer system, increasing pumping and treatment costs without generating revenue. Common entry points include:

• Cracks or breaks in sewer lines
• Leaking manholes, especially in low-lying areas prone to flooding
• Storm drains or downspouts improperly connected to the sewer system

Many sewer systems rely on pumping stations to convey wastewater to treatment plants. Excess I&I increases pumping costs and treatment requirements, adding labor, chemical, and energy expenses. During heavy rainfall, I&I can result in thousands of dollars in additional monthly costs. Severe I&I may even push treatment plants to capacity, necessitating costly plant expansions.

Strategies to Reduce I&I

Utilities can take several steps to identify and reduce I&I:

• Manhole adjustments: Raise or relocate low-lying manholes. Inspect manholes during rain to detect groundwater entry. Repair or replace leaking manholes.
• Sewer line inspections: Use cameras to inspect lines for leaks. Cameras can be purchased, rented, or shared among nearby cities. Contractors can also provide line filming services.
• Prioritization: Establish a priority list for repairing or replacing leaking lines.
• Smoke testing: Identify storm drains and downspouts connected to the sewer system. Property owners should be notified to disconnect these connections; non-compliance may result in citations under city sewer ordinances.

Through these methods, utilities can significantly reduce I&I, lowering operational costs and preserving system capacity.