If a water system's unaccounted for water loss exceeds _______, a system wide leak survey should be conducted.

• A. 5%
• B. 15%
• C. 25%
• D. 10%

Answer: (B)

Unaccounted-for water represents losses in the system that aren’t reflected in billed customers’ usage—things like undetected leaks, metering errors, or unauthorized connections. When these losses rise to a moderate level, it signals that leaks may be spread throughout the distribution system rather than confined to one area. That’s when a system-wide leak survey becomes appropriate: a coordinated effort to locate and verify leaks across the entire network using methods such as acoustic leak detection, pressure surveys, and meter audits. The idea is to systematically find and fix the sources of loss to reduce water waste and protect service reliability.

In practice, utilities often use a mid-range threshold—about 15% of total water produced—as the point at which a comprehensive leak survey is warranted. This level suggests meaningful, systemic losses rather than minor accounting discrepancies. Lower thresholds may miss diffuse leaks, while much higher thresholds imply more extreme, urgent conditions.

Calculation-wise, unaccounted-for water is the difference between water produced and water delivered (billed and authorized unbilled uses).