As a rule, large modern industrial complexes are significant water users. This raises the problem of providing them with reliable and sustainable water supply systems. To solve this problem, relatively small, special reservoirs for technical water supply are often created. When creating them, it is a priori assumed that their water masses will be comparatively homogeneous over the aquatorium and throughout the depths, and so, therefore, that their flushing can be successfully used to prevent a possible accumulation of pollutants. The experience of operating such reservoirs in the Verkhnekamsky potassium and magnesium salt development zone in Ural, Russia, has shown that, due to intense diffuse pollution, the reservoirs are characterized by significant vertical non-uniformity, fundamentally altering the hydrodynamics of these water bodies. Based on a series of research, including field observations and computational experiments, the present paper reveals that the vertical non-uniformity of water masses plays a key role in ensuring the sustainability of technical water supply.