PUBLIC UTILITIES ADVISORY BOARD AGENDA ITEM
ACTION REQUESTED:
title
Receive the Annual Non-Revenue Water Update - Water Year 2025
body
DEPARTMENT: Water Utilities
SUBMITTED BY: Darrell Blenniss, Director Water Utilities
BOARD/COMMISSION REVIEW:
N/A
BACKGROUND:
As a permittee of Lake Michigan water, the City of Naperville is required to submit an annual Water Loss Audit to the IDNR. This audit serves as the primary metric for ensuring the efficient use of the region's most critical natural resource. The audit is conducted using the American Water Works Association (AWWA) M36 methodology, which provides a standardized framework for tracking water flow through the distribution system.
Regulatory compliance requires utilities to maintain a Non-Revenue Water (NRW) rate generally below 10%. Exceeding this threshold can result in regulatory scrutiny and mandatory compliance plans.
The table below illustrates the improvements that resulted from the increased focus on the reduction of non-revenue during the past water years.
|
Water Year |
Non-Revenue Water % |
ILI |
5 Year Rolling Average (NRW) |
5 Year Rolling Average (ILI) |
|
2022 |
14.8% |
1.93 |
13.1% |
1.65 |
|
2023 |
16.1% |
.77 |
13.7% |
1.52 |
|
2024 |
3.8% |
.10 |
12.2% |
1.28 |
|
2025 |
3.3% |
.01 |
10.2% |
0.92 |
DISCUSSION:
1. Water Year 2025 Performance
For the reporting period of October 2024 through September 2025, Naperville Public Utilities demonstrated exceptional system performance:
• Total Water Supplied: 4,992.583 Million Gallons (MG)
• Authorized Consumption: 4,890.207 MG
• Non-Revenue Water (NRW) Rate: 3.3%
This 3.3% NRW rate places Naperville in the top tier of Lake Michigan communities, significantly outperforming the regional average and comfortably exceeding IDNR compliance standards.
2. Data Reliability & System Integrity
The audit process includes a "Data Validity Score" to assess the confidence level of the input data. Naperville achieved a score of 89 out of 100 (Level IV), indicating that the utility’s data collection practices are robust and reliable for strategic decision-making.
3. Infrastructure Leakage Index (ILI) Analysis
The audit yielded an Infrastructure Leakage Index (ILI) of 0.01. The ILI is a ratio of current real losses to the theoretical minimum achievable leakage.
• Standard Target: An ILI between 1.0 and 3.0 is considered optimal for a well-managed system.
• Naperville’s Result (0.01): While technically categorized as "World Class," a score near zero is statistically anomalous for a system of our size (691 miles of main).
Strategic Interpretation:
This ILI score indicates that the City’s physical infrastructure is extremely tight, with negligible "Real Losses" (physical leaks). However, the result also suggests that the current audit model may be over-attributing water volume to "Apparent Losses" (metering inaccuracies and data handling). Essentially, the model is accounting for so much potential meter error that it calculates near-zero physical leakage to balance the water equation.