Quality of Drinking Water in the Don River Delta under Conditions of a Low Water Level

The low level of water and regulation of the Don River runoff led to an irreversible transformation of natural hydrological and hydrochemical processes. At the end of 2022, despite the shortage of river water, the region began laying a water pipeline with a capacity of up to 300 000 m(3) of water per day to the Donbass. Are there enough water reserves for the increasing economic needs throughout the year? This work is based on a targeted study of the chemical composition of water under different regimes and sea levels on the Taganrog seashore of the Don Bay and delta. The experiment covers the period from December 2, 2022, until January 30, 2023, and single measurements, for comparison, on February 21, March 30, and April 17, 2023. In total three types of ionic composition typical of the Svinoe delta arm of the Don River are distinguished: first, marine with a dominant (>80%) total amount of sodium and potassium ions, chlorides, and salinity up to 7-9 g/L. Second, the waters of the Don correspond to low salinity (<2 g/L), an increased proportion of Na+ + K+ (50-60%), and a close amount of SO42- and HCO3- (30-40% each). Third, since 2018, groundwaters have been regularly recorded when the level decreases. These are medium brackish waters with a salt content >5 g/L. They typically have a high content of sodium and potassium (>60%) and sulfate ions (60-80%). Monitoring shows that the deficit of fresh drinking water will increase, and with increasing withdrawal of water, the deficit will accelerate in time. It will be replaced (up to 5-7 g/L) by mineralized groundwater and water from the Black Sea. The proportions of slightly brackish (2-4 g/L) and medium brackish (4-8 g/L) waters to be pumped (redistributed by seasons) into water pipelines still need to be explored.