Abstract <p>The quality of natural and conditioned water is traditionally characterized by average indicators of its composition and properties. For many tasks of water management, this is insufficient, and it is necessary to take into account the amplitude and frequency of fluctuations in pollutant concentrations in a wide range of frequencies, including subhourly ones. According to existing concepts, such variability should be softened during water purification. However, this work substantiates that during water treatment, not only may the variability of impurity concentrations be preserved, but it may also increase, partially reproducing the dynamic characteristics of source natural water. Although the distribution function of the concentration of the controlled impurity is transformed during the water purification (conditioning) process, but, as shown by the example of measuring the content of fine particles (turbidity), the structural and dynamic properties of natural water are preserved. To prove this important circumstance in theoretical and applied terms, methods of statistical analysis of time series of turbidity of natural water and water conditioned by coagulation and filtration are used. It is shown, in particular, on representative arrays of subhourly experimental data obtained in the different periods of the water regime of the rivers in the basins of the Pacific and Arctic Oceans that as a rule, conditioning increases rather than decreases the coefficient of variation of turbidity. At the same time, coefficients of determination in quantile-quantile plots that are close to unity are observed and cause-and-effect relationships are preserved between the controlled indicators of the water received for treatment and the purified water.</p>