Assessment of changes in hygienic indicators of drinking water from сentralized water supply systems during transportation

BACKGROUND: Although the majority of drinking water from centralized water supply systems meets the established standards, its quality still may be compromised during its transportation to the end user via pipeline systems.

AIM: To assess the changes in the composition of drinking water from centralized water supply systems during transportation with the Primorsky Territory as an example.

MATERIALS AND METHODS: The findings of the 2016–2022 laboratory studies conducted by the Center for Hygiene and Epidemiology in the Primorsky Territory as part of the social and hygienic monitoring program (189 monitoring points) were subjected to analysis. The pre- and post-distribution network data were compared using Microsoft Office Excel. The analysis of 18 indicators (19,485 pairwise comparisons) was conducted using IBM SPSS Statistics, while spatial visualization was performed with ArcGIS 10.8.2.

RESULTS: Among the hygienic indicators, the color of water significantly (p=0.005) intensifies after passing via the water supply pipeline system. Correlation analysis indicates that the color intensification may be attributed to the oxidizability of iron, manganese, and permanganate (r=0.28; r=0.21; r=0.13 at p <0.05, respectively). The hydrogen index demonstrates a tendency to shift towards an acidic medium, particularly during the summer months (χ²=14.5; p=0.002). The assessment of the influence of the water dispenser type revealed a tendency of the iron and some microbiological indicators to accumulate in standpipe systems, while the concentrations of these indicators were found to be decreased in building taps. The indicative significance of the microbiological indicators (generalized coliform bacteria, E. coli, enterococci) was recently highlighted in regulatory documents on the hygienic assessment of water quality. These bacteria are more frequently found in the distribution network than the nowadays excluded coliform bacteria, both general and thermotolerant. A spatial analysis of the proportion of drinking water samples that deteriorate during transportation enabled the identification of the water supply systems in the region where transportation represents a significant factor influencing the deterioration of water quality.

CONCLUSION: The retrospective analysis of the changes in the composition of drinking water from centralized water supply systems during transportation identified the indicators that are most susceptible to changes. This can be used when planning the upgrade of the water supply and treatment systems.