Describing water treatment process performance: Why average log-reduction can be a misleading statistic

Area of Science:

• Environmental Science
• Microbiology
• Public Health

Background:

• Log-reduction quantifies pathogen removal in water treatment, crucial for safe drinking water.
• Averaging log-reduction values is a common practice to summarize treatment performance.
• Misinterpretation of averaged log-reduction can impact safety assessments.

Purpose of the Study:

• To mathematically demonstrate that averaged log-reduction values overstate treatment performance.
• To highlight the consequences of using averaged log-reduction in risk analyses.
• To introduce effective log-reduction as a more accurate summary statistic.

Main Methods:

• Mathematical proof to analyze the statistical properties of averaged log-reduction values.
• Comparison of averaged log-reduction with effective log-reduction.
• Analysis of implications for risk assessment in water and food safety.

Main Results:

• Averaging log-reduction values characteristically overstates the actual average performance.
• Higher reported average log-reduction does not guarantee higher average performance.
• Risk analyses using averaged log-reduction can underestimate average risk significantly.

Conclusions:

• Averaged log-reduction is a misleading metric for water treatment performance.
• Effective log-reduction provides a more accurate representation of average treatment efficiency.
• Accurate performance metrics are essential for ensuring public health and safety.