Comparative Hygienic Assessment of Qualitative Composition of Drinking Water of Centralized Water Supply System in Certain Districts of Ryazan

Abstract

INTRODUCTION: Providing the population with drinking water that meets national standards is one of the urgent problems. In connection with the use of ground and surface waters for water supply in Ryazan and their different proportions in the water supply system, the quality of drinking water in individual districts of the city may have special features. AIM: Comparative hygienic assessment of the qualitative composition of drinking water of the centralized water supply system in the residential districts of Ryazan. MATERIALS AND METHODS: The results of laboratory quality control of drinking water of central water supply system for the period from 2012–2021 were analyzed according to the monitoring data of the Center for Hygiene and Epidemiology in the Ryazan Region. The calculation of the average many-year concentrations and the percentage of samples that do not meet hygienic requirements, was carried out. For statistical processing, the method of analysis of variance and Scheffe and Tamhein tests for paired comparisons were used, taking into account the results of Levene test. Statistical parameters were calculated in SPSS Statistics 19 software. RESULTS: Excess hardness of drinking water was recorded in all districts of the city, with the proportion of such samples ranging from 0.8% (Solotcha) to 74.1% (Stroitel). The average value of the total water hardness in Stroitel district was the highest, 7,554 mg-eq./l, exceeding the hygienic norm. In most districts, with the exception of Kanishchevo, Diagilevo, Zheleznodorozhny and Sovetsky, water samples (0.9–2.7%) were recorded that did not meet hygienic requirements for the content of generalized and thermotolerant coliform bacteria. The average many-year concentration of iron (2+) in the drinking water of the centralized water supply system of the village of Solotcha 2.5 times exceeded the MPC (0.3 mg/l) and was significantly higher than in the compared territories, and in 64.6% of samples its one-time concentrations did not correspond to the hygienic norm. In the territories of the districts: Dashkovo-Pesochnya, Kanishchevo, Mirny, Sovetsky and Zheleznodorozhny, the proportions of water samples with one-time concentrations of aluminum exceeding the MPC (0.2 mg/l) ranged from 1.5% (CI 95%; 0.3–8.2%) to 6.1% (CI 95%; 2.4–14.6%). One-time concentrations of boron above the MPC (0.5 mg/l) were recorded in drinking water in all districts of the city with the exception of Diaghilevo and Oktyabrsky, and ranged from 1.0% (CI 95%; 0.2–5.2%) to 1.9% (CI 95%; 0.52–6.68%). The average many-year concentration of cadmium in the drinking water of Dashkovo–Pesochnya residential area was 0.0006 mg/l and 1.9-14 times exceeded that in other districts of the city (p < 0.05), while the proportion of water samples where one-time concentrations of this toxicant exceeded the MPC (0.001 mg/l) was 4.7%. Also, cadmium concentrations exceeded the hygienic standard at the control points of water supply network in Mirny (in 2.9% of samples), Sovetsky and Zheleznodorozhny districts (0.9% of samples in each). One-time concentrations of nickel most often exceeded the respective MPC (0.02 mg/l) in the drinking water of Dashkovo-Pesochnya and Solotcha residential areas making 10.9% (CI 95%; 4.7–23.0%) and 11.1% (CI 95%; 4.8–23.5%), respectively, and least often of Mirny and Moskovsky areas — 2.2% (CI 95%; 0.4–1.3%) (p > 0.05). CONCLUSIONS: The territorial features of the qualitative composition of drinking water of the centralized water supply system of the city of Ryazan are determined, consisting in higher average values of individual parameters and the percentages of samples that do not meet hygienic standards for hardness in Stroitel, Sovetsky, Zheleznodorozhny and Dashkovo-Pesochnya districts; for the content of sanitary-indicative microorganisms — in Stroitel, Dashkovo-Pesochnya, Mirny and Oktyabrsky; for the iron content (2+) — in Stroitel, Zheleznodorozhny, Oktyabrsky, Kanishchevo and Solotcha; for boron — in Stroitel; for cadmium — in Dashkovo-Pesochna and Mirny; for nickel — in Dashkovo-Pesochna and Solotcha; for lead — in Stroitel and Mirny.