Аннотация:Structural features of pure water and aqueous solutions of the electrolytes NaCl, NaCO3 and Zn[NO3]2 were comprehensively studied using the X-ray diffraction, infrared absorption spectroscopy and Raman spectroscopy methods. Spectral in situ measurements of the test samples at pressures up to 1000 bar and temperatures 25 – 500 oC were performed with the use of the high-temperature high-pressure cells with transparent sapphire windows. It was experimentally determined a temperature and pressure impact on the infinite clusters of the hydrogen-bound molecules that is inherent to the liquid water. Therewith, the critical isotherm of the liquid water is defined as the conditional boundary of the percolation threshold below which the clusters of finite sizes can exist only. An evaluation of the effect of the electrolytes, dissolved in water, onto the hydrogen bonds and structural features of water of the aqueous solutions as well as determination of the polyatomic anions stability under high temperatures and pressures was also performed. The vibrational spectra of NaCl are not revealed a significant difference between the properties of the aqueous solution and pure water under the test conditions.