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The timely restoration of water treatment devices is a prerequisite for sustainable water supply to consumers. Difficulties in estimating the moments of such recovery are associated with variability in the failure rate of mechanical systems. In this regard, two statistical approaches are proposed in this paper for scheduling the frequency of such recovery: estimating the constant frequency of maintenance for different groups of identical devices or systems (standard maintenance) or evaluating this frequency from the actual performance of individual devices (state maintenance). It is shown what approach should be used depending on the goal: to prevent devices from operation with expired service life or to make better use of the resource capabilities of these devices. It is also shown that the actual service life may significantly differ from its average value for groups of similar systems due to the influence of variability in the composition of source water and the characteristics of working units. Some limitations and recommendations on the practical implementation of forecasting the moments of unacceptably high losses in the performance-controlling parameter of water treatment devices and systems are considered. The novelty of this study is that it is based on the provisions of reliability theory, which provides a substantiated approach to the formation of a maintenance regime: the matter that becomes more urgent when designing water treatment technologies and equipment operation. The transition to these provisions, even in “advanced” areas of technology such as aerospace industry, encounters a number of difficulties, which the authors have managed to overcome in the case of water use problems to recommend the relevant specialists to pay attention to the potential efficiency of this approach and its use in the practice of operating water treatment devices and systems.

The indicators of the composition and quality of natural water are random variables. Since the “linear” approach to their assessment and forecast provides no acceptable results, it necessary to take the nonlinearity of natural hydraulic systems into account. We have made a nonlinear logistic description of the variations in the concentration of pollutants, making it possible to assess the water composition depending on the intensity of its pollution and self-purification. Based on the results obtained, we have revealed cyclic fluctuations of the indicators monitored with amplitude decreasing at a low pollution rate and increasing with its rise. Occasionally, they are accompanied by bifurcations with a further transition to complete chaos.

Experimental data are presented to show that the spatial and temporal variability of the composition of river waters cannot be explained solely by the influence of sources and effluents of the substances and that there are additional significant factors that support or even initiate the dispersion of the concentration of pollutants here. This variation is reflected in the resources and the economic characteristics of the rivers; so identification of its reason is important. Thus, the hydrodynamic structure of the water flow is studied by analyzing the complete system of equations of fluid motion mechanics. The completed work allowed us to show that the elements of this structure are waves, vortices, and highly gradient layers (ligaments), presumably creating the described dispersion effect. Further investigation of the relationship of the precise hydrodynamic and hydrochemical structures of river waters will contribute to better understanding of the water-environmental processes, ensuring the perfection of water management methods.