Today, one of the urgent problems is contamination of drinking water due to the intensive development of industry and transport, which implies bringing ever-increasing amounts of harmful substances into the natural environment. A modern city is a complex source of anthropogenic strain on the environment, so the problem of drinking water quality is multidimensional, and it affects many aspects of human life [1−6]. The health of the population depends on the quality of water, on the daily intake of trace elements and minerals [7−9].

In general, the condition of water bodies, especially surface ones, is deteriorating. Rivers are one of the main sources of drinking water, but they are polluted, ad purification of water from them requires multifunctional filters [10, 11]. For many years now, the government reports have been assess the sanitary and epidemiological condition of water bodies that are used for drinking purposes as polluted or even contaminated [6, 12, 13].

The hygienic standards that entered into force in 2021 (SanPiN 2.1.3684 "Sanitary and epidemiological requirements for the maintenance of urban and rural settlements, for water bodies, drinking water and drinking water supply, atmospheric air, soils, living quarters, operation of industrial and public premises, organization and conduct of sanitary and anti-epidemic (preventive) measures", SanPiN 1.2.3685-21 "Hygienic standards and requirements for ensuring the safety and (or) harmlessness of environmental factors for humans") impose stricter requirements on the organization of laboratory quality control of drinking water supplied to the population [14]. Improving the quality and reliability of drinking water supply to the population is one of the urgent social problems, since the health of the population largely depends on how safe their drinking water is [7, 15].

There are several factors and conditions that, combined, bring about underground water supply sources, including intersecting aquifers and concave landforms, certain geological and structural features of the area, and filtration heterogeneity of the water-bearing material [16, 17].

Trace elements migrating from the soil into the water largely shape its composition. The conditions of such migration are one of the most difficult subjects: it is a continuous process the rate of which is determined by the thermodynamic environment [18]. It has always been believed that water is involved in all geochemical processes, including migration, destruction of rocks, and release of trace elements.

Unlike surface waters, groundwater is well protected from various kinds of anthropogenic pollution [19], but its closeness to artificial reservoirs can negatively affect water quality.

One of the key pollutants of groundwater is return water with its increased mineralization, high content of mineral fertilizers, pesticides, and industrial waste, which boosts the overall hardness of the aquifer [16, 17, 20]. The peculiarities of the formation of the qualitative composition of groundwater may require an integrated approach to the purification of water drawn therefrom before it is supplied to the public.

Violation of regulations concerning the sanitary and epidemiological well-being of the population creates a potential risk of harm to health, including various infectious and non-infectious diseases [21, 22].

The above supports the relevance of further investigation of the hygienic features of groundwater formation conditions.

This study aimed to assess the hygienic quality of water intended for future use, taking into account the characteristics of the underground aquifer.

METHODS

Through the lens of the hygienic properties, we assessed the priority risk factors of drinking water using statistical forms and reports that describe the sanitary and epidemiological state of the region.

The quality of water supplied in Voronezh was evaluated through retrospective epidemiological studies that factored in the changing anthropogenic and hydrogeological conditions. We analyzed samples of drinking water taken both at Voronezh water lifting stations and from the water supply network, and statistically processed 1200 water sample laboratory control protocols (samples from the supply network) and 850 protocols reflecting the quality of water collected at the lifting stations. The data were processed as prescribed in GOST R 59024-2020 "Water. General requirements for sampling", with estimation of the confidence interval and confidence probability.  The studied parameters were graded against the requirements of SanPiN 1.2.3685-21 "Hygienic standards and requirements for safety and/or harmlessness of an individual's environment".

For statistical data analysis, we used Microsoft Excel (Microsoft, USA). We calculated the mean (M) and relative values, the standard error (m), and established the significance of differences using Student's t-test and the chi-square (χ2) at p < 0.05.

RESULTS

In the context of implementation of the Clean Water Federal Project of the Housing and Urban Environment National Project, Voronezh Region realizes the State Program "Provision of high-quality housing and communal services to the population of the Voronezh Region in 2025"; one of the key target indicators of this Program is "the proportion of the population provided with high-quality drinking water from the centralized drinking water supply system".

The main source of drinking water in Voronezh is the groundwater of the Neogene-Quaternary aquifer. Its water-bearing material is inequigranular sand. The thickness of these deposits is 40−50 m.

The depth of the exploited aquifer ranges from 10 to 80 m. Under the classification of water supply sources, this aquifer belongs to the upper zone. Consequently, exchanges water with other bodies actively and is poorly protected from anthropogenic pollution.

Analysis of the water showed that its mineralization ranged from 0.18 to 0.47 g/dm³. In the studied region, mineralization is determined by such components as sulfates, bicarbonates, calcium and magnesium. The role of chlorides is insignificant.

Based on the studied chemical composition of the drawn groundwater, four geochemical types of water have been identified:

- calcium-magnesium;

- calcium sulfate;

- mixed;

- calcium-sodium.

The analysis showed significant fluctuations in the concentration of iron and manganese throughout the year, season-dependent. The maximum content was registered from March to September (figure).

The most common well design in the region:

• depth from 74 to 80 m;
• working part 12 m;
• the mesh strainer with gravel filling.

All wells are equipped with hermetically sealed holes in the strainer column for measuring the dynamic water level, and a sampling tap for sanitary and chemical analysis. Pavilions protect the well heads from contamination; the heads themselves are in a sunken well. There are also designated sanitary protection zones, which contribute to the preservation of water quality.

The drinking water supplied to the population is purified by nonchemical deironization using simplified aeration followed by filtration and neutralization.

Laboratory tests conducted in recent years (2019–2023) revealed that the water meets hygiene standards for most indicators, except for total hardness, iron, manganese, and nitrates. Hardness is defined by a set of physical properties and chemical components related to the content of alkaline earth metal salts dissolved in the water, mainly calcium and magnesium. They are also called the "hardness salts."  Water acquires calcium through the dissolution of limestone and gypsum. Magnesium enters the water during the dissolution of dolomites (MgCO3 + CaCO3) under the action of carbonic acid from the water itself.

Every year, the concentration of iron and manganese compounds in the water is registered as increased.

A retrospective analysis of the aquifer water quality showed that the levels of these compounds were first registered above the expected values in 1972, which gives reason to associate this fact with the adjustment of flow of the Voronezh River. The Voronezh Reservoir was built in 1972, and it affected the sanitary and hygienic conditions of water bodies. The area for the Reservoir is in the zone of high anthropogenic load, and its construction was accelerated. From the hydrotechnical viewpoint, the body has acquired the properties of a shallow lake with slow water exchange.

The quality of water in this artificial reservoir deteriorated rapidly due to slow water exchange and purification, which translated into the increased deposition of sediments. These sediments have good conditions for accumulation of heavy metal salts.

The situation lead to the deterioration of the aquifer water used for drinking purposes.

The adverse effect of the reservoir on the quality of water supplied to the city's population was confirmed by the locations of the lifting stations: the further away from the reservoir they were, the better the water was.

Currently, the reservoir's water is partially used as process water, for irrigation and landscaping of the coastal recreation zone. However, there is still no solution that would allow rationally using groundwater for drinking purposes only and water from surface bodies — for industrial purposes.

DISCUSSION

The construction of an artificial reservoir within the city limits changed the natural geochemical background, which altered the volumes and the rate of migration of iron and manganese.

The reservoir, which was originally created to provide process water to industrial facilities in the region, has become a receiver for a huge amount of domestic, industrial and stormwater runoff.

The results of the study, the analysis of regulatory legal acts, and the data from the scientific literature [8, 11, 23, 24] show that the quality of drinking water and the general condition of domestic drinking water supply cannot be considered without taking into account anthropogenic interference with the natural status of the environment.

Microbiological monitoring of drinking water should also be continuous, since microorganisms are a direct indicator of environmental pollution and its sanitary and epidemiological condition.

Some of the priority areas related to the provision of the population of the regional center with adequate quality water could be:

- the use of such sources of water supply that would not be exposed to the reservoir;

- reconstruction of the existing sewage treatment plants, which collect both industrial and domestic wastewater for subsequent purification and discharge into the reservoir;

- improvement of the drinking water treatment system with its purification at the lifting stations;

- effective control over the establishment of sanitary protection zones for underground water supply sources;

- careful attitude to the preservation of the necessary volumes of drinking water, excluding its use for technological purposes;

- use of collective and individual household filters for additional cleaning;

- timely updating of the water pipeline transportation system from the intake to the distribution network.

CONCLUSIONS

The creation of the reservoir was a trigger for the accumulation of large amounts of pollutants (iron and manganese compounds) in the sediments, which requires an integrated approach to its protection as well as management decisions to ensure the sanitary and epidemiological well-being of the population.

In order to bring the water supplied to the population up to hygienic requirements, it is necessary to implement new approaches to water purification and disinfection using nanoreagents, synthetic and natural nanosorbents. To optimize the city's drinking water supply, the following measures will be appropriate: finding water supply sources that will not be affected by the reservoir; using the underground aquifer only for drinking purposes, excluding use for process needs; improving the reliability of the water supply system through the implementation of technological, water protection and sanitary measures.