High quality organization of water supply to the population is essential for prevention of multiple disorders, including the communicable diseases [1]. Numerous epidemiological data from both past (late 19 — early 20 century) and modern periods show the relationship between the incidence of infections and invasions transmitted by fecal‑oral route and the state of water supply [2–5].

In Russia, public water supplies are a branched network of the water intake, water treatment, and water distribution facilities, some of which need repair and renovation.

According to SanPiN 2.1.3684–21 “Sanitary and Epidemiological Requirements for the Maintenance of Urban and Rural Settlements, Water Facilities, Drinking Water and Drinking Water Supply, Atmospheric Air, Soils, Living Quarters, Operation of Industrial, Public Premises, Organization and Conduct of Sanitary and Anti‑Epidemic (preventive) Measures”, water from the water‑supply sources can be used for drinking and domestic use in case of compliance with the requirements for drinking water. In case of non‑compliance with the hygienic standards of the quality of water from the water‑supply sources used as public sources of drinking water supply, water treatment should be used to ensure the quality and safety of water in the distribution network in accordance with the hygienic standards [6].

The study was aimed to assess the impact of the quality of water from water bodies on morbidity in the population of the Russian Federation based on the analysis of the relationship between the microbiological and parasitological parameters of water quality and the incidence of enteric infections and invasions in the population.

The research tasks included:

• assessing microbiological parameters of the quality of water from the sources of domestic water supply (grade I reservoirs);
• assessing microbiological parameters of the quality of water in waterworks before entering the distributive pipelines;
• assessing microbiological and parasitological parameters of the quality of water from water‑supply sources;
• assessing microbiological parameters of the quality of recreational water (grade II reservoirs);
• assessing the incidence of acute enteric infections and invasions (giardiasis) in the population.

METHODS

The study involved the use of data from the State reports “On the State of Sanitary and Epidemiological Well‑Being of the Population of the Russian Federation” issued by the Federal Center of Rospotrebnadzor in 2011–2020. Statistical processing of the data was performed using Microsoft Excel.

RESULTS

According to the study, in 2011–2020, the average share of off‑nominal tests (based on the microbiological parameters of water samples collected from grade I reservoirs) was 17.19%, and showed a moderate downward trend (Rav.gr. = –1.28%) (fig. 1).

The percentage of off‑nominal tests for water samples collected from waterworks before entering the distributive pipelines was 2.90%, and showed a pronounced downward trend (Rav.gr. = –7.02%) (fig. 2).

The reported decline in the share of off‑nominal microbiological tests of water samples collected from waterworks before entering the distributive pipelines compared to that of water from the surface water‑supply sources may be interpreted as evidence of the relatively high quality water treatment in the majority of waterworks in Russia.

The percentage of positive tests of water samples collected from the centralized sources of water supply was 3.50%; a pronounced deceleration of the growth rate was observed (Rav.gr. = –5.97%) (fig. 3). This value is marginally higher than the percentage of positive tests of water samples collected from waterworks before entering the distributive pipelines, which indicates no significant effect of the state of water distribution pipelines on the parameters of the drinking water microbiological quality.

Parameters of the microbial composition of water from the centralized sources of water supply correlate with the microbiological quality of water in waterworks before entering the distributive pipelines (R_xy = 0.98).

Analysis of the dynamic changes in microbiological quality of water over the past 10 years indicates a slight decline in the share of off‑nominal tests of water samples collected from grade I reservoirs during the studied period. Furthermore, a significant decrease in the number of positive tests of water samples collected before entering the distributive pipelines and from the distributive pipelines during the same time period is observed. This may be interpreted as evidence of the improvement in the quality of waterworks performance in Russia over the past few years.

According to literature, chlorination and ultraviolet light that are used to disinfect water in waterworks have a harmful effect on the bacterial flora, however, these do not provide sufficiently effective Giardia cyst inactivation [7, 8]. Considering this fact, it was interesting to analyze the data from the State reports on the content of this protozoan species in drinking water.

According to the study, the average share of off‑nominal tests of water samples collected from the centralized sources of water supply (based on the presence of Giardia cysts) was 0.06%; a moderate downward trend was observed (Rav. gr. = –8.63%) (fig. 4).

Despite the above literature data on the insufficient effect of standard water disinfection methods on Giardia cysts, our study revealed a strong correlation between the percentage of off‑nominal microbiological tests of water samples collected from the centralized sources of water supply and the number of samples containing Giardia cysts (R_xy = 0.84).

The average share of off‑nominal tests (based on the microbiological parameters of water samples collected from grade II reservoirs) was 22.76%, and showed a moderate downward trend (Rav.gr. = –2.25%) (fig. 5). This indicator corresponds in some ways to the results for water from grade I reservoirs.

The average incidence of acute enteric infections (AEI) in Russia over the studied 10 years is 521.1 per 100,000 population, and shows a moderate downward trend (Rav.gr. = –2.77%) (fig. 6).

The incidence of acute enteric infections correlates with the percentage of off‑nominal microbiological tests of water samples collected from the centralized sources of water supply (R_xy = 0.49) and water samples collected from grade II reservoirs (R_xy = 0.56), which is in line with the literature data on the epidemiological role of water [5].

Information about the incidence of certain enteric infections and its trends is provided in table. Analysis of this information has revealed a positive correlation between the incidence of such bacterial infections, as dysentery (R_xy = 0.96) and salmonellosis (R_xy = 0.94), hepatitis A virus (R_xy = 0.61) and the percentage of off‑nominal microbiological tests of water samples collected from the centralized sources of water supply. No correlations between the percentage of off‑nominal microbiological tests of water samples collected from the centralized sources of water supply and the incidence of viral enteric infections (except hepatitis A virus) have been revealed, possibly due to the fact that disinfectants used for water treatment mostly affect bacterial flora. This provision is also in line with literature data [5].

The average incidence of giardiasis in the Russian Federation over 10 years is 34.7 per 100,000 population; a pronounced downward trend is observed (Rav.gr. = –10.40%).

There is a strong correlation between the incidence of giardiasis and the percentage of off‑nominal tests of water samples collected from the centralized sources of water supply based on microbiological (R_xy = 0.98) and parasitological (R_xy = 0.87) parameters.

Discussion

The results obtained based on the averaged data from the large territory of the Russian Federation make it impossible to draw reliable conclusions. However, it is possible to formulate the basic provisions that arise from the findings:

• based on microbiological parameters, the quality of water from the centralized sources of water supply in the Russian Federation is generally consistent with the quality of water in waterworks before entering the distributive pipelines; this may be interpreted as evidence of the rather good state of the distributive pipelines having no sufficient effect on the quality of water supplied to the population;
• the observed correlation between the percentage of off‑nominal tests of water samples collected from the centralized sources of water supply (based on the presence of Giardia cysts) with the percentage of water samples non‑compliant with the hygienic standards based on microbiological parameters may be interpreted as evidence of the sufficient effect of water treatment on pathogenic protozoa in most of Russia;
• the findings confirm the literature data on the impact of biological water contamination on the incidence of enteric infections (especially bacterial) and invasions in the population.

CONCLUSION

The main provisions of the study make it possible to conclude that maintaining the sanitary and hygienic condition, as well as providing thorough sanitary and hygienic control of water bodies is relevant.