Document Type : Technical Note
Authors
1
Director of Water and Wastewater Quality Monitoring and Supervising Center, Company of Water and Wastewater of Tehran Province, Tehran, Iran
2
Head of Calibration and LIMS of Reference Laboratory, Company of Water and Wastewater of Tehran Province, Tehran, Iran
3
Quality Control Expert of Reference Laboratory, Company of Water and Wastewater of Tehran Province, Tehran, Iran
4
Member of the Board of Directors of Payesh Salamat System Company, Tehran, Iran
10.22093/wwj.2026.489323.3454
Abstract
Conformity assessment of drinking water quality test results, particularly under critical water supply conditions, requires decision rules approaches that both protect consumer health and prevent unjustified rejection of acceptable water sources. In this study, conformity assessment and decision rules based on measurement uncertainty, were investigated for the acceptance or rejection of Nitrate, Turbidity, and pH test results in drinking water. These measurands were selected due to their importance in water quality and their direct or indirect impacts on human health. The primary objective of this research was to determine the probability of conformity of test results with regulatory requirements and to highlight the role of measurement uncertainty in reducing the risk of incorrect decisions, especially when new water sources are introduced into the distribution network. Nitrate, Turbidity, and pH analyses were conducted in accordance with the latest edition of the Standard Methods for the Examination of Water and Wastewater. Measurement uncertainty was estimated separately for each measurand, and conformity assessment was performed with reference to the permissible limits specified in the Iranian National Drinking Water Standard No. 1053. Based on these inputs, the probability of conformity for each test result was calculated and used as the basis for acceptance or rejection decisions. The results demonstrated that applying a decision rule based on measurement uncertainty can significantly influence conformity assessment outcomes for drinking water quality parameters. The calculated probabilities of conformity were 95% for Nitrate, 90% for Turbidity, and 85% for pH, indicating different levels of decision confidence for the three measurands. These differences suggest that for certain measurands-particularly Nitrate, which has a more direct impact on human health-the risk of incorrect decision rules is higher, and measurement uncertainty must be considered more rigorously when declaring conformity. The findings further indicate that reliance solely on raw measurement results, without incorporating measurement uncertainty, may lead to the incorrect acceptance of unsafe water sources or the unjustified rejection of compliant ones. Overall, this study emphasizes that implementing a measurement uncertainty-based approach in the conformity assessment of drinking water test results enables informed decision rules with defined and acceptable risk levels. Adoption of this approach enhances decision accuracy, reduces risks to consumer health, prevents unnecessary rejection of acceptable water resources, and contributes to more efficient resource utilization and avoidance of unnecessary costs in water supply management systems.
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