River waters hardness variations on the territory of the republic of Tatarstan.

One of the main criteria for river water quality is overall hardness, the value of which determines its suitability for use in various sectors of the national economy.Availability of the many-year information about the magnitude of the overall hardness of the river waters of the Republic of Tatarstan served as the basis for analyzing its changes in time and space. As an integral indicator, the average annual value of the overall hardness is chosen, the distribution of which throughout the territory of the Republic is clearly reflected in the given skeleton maps. A comparative analysis of the total hardness of river waters, observed in the XX and XXI centuries, showed that its value remained within the category of moderate, medium hardness and hard waters, but there was a redistribution of these values in space. Since the formation of rigidity largely depends on local features of the territory and, first of all, on the heterogeneity of the geological structure of the basin, the analysis of its changes was made commensurate with the geological structure of the three large geographical regions of the Republic of Tatarstan − Pre-Volga, Pre-Kama and Zakamye.The formation of hardness is also influenced by the anthropogenic factor. In the zone of influence of large reservoirs, created in the territory of the Republic of Tatarstan, a rise in the level of groundwater is observed, changing not only the nature of the underground supply of water bodies of the Republic, but also the quality of river water. The redistribution of general hardness in the south-east of the republic is connected with the activities of oil enterprises, which make significant adjustments to the hydro/chemical composition of natural waters.