In this research, the E. coli stress response on the in vivo hypoosmotic shock has been studied. E. coli was grown in a high osmolarity medium (125 mM – 650 mM sodium chloride) and then rapidly transferred into the low osmolarity medium (0 mM sodium chloride). For this purpose different strains were used: wild type, double mutant (ΔmscSΔmscL) and the ΔaqpZ mutant. Based on the single cell results of the fluorescence microscopy and the data analysis, it has been observed that wild type and the mutant cells volume was increased for 7 – 18%, proportionally to the shock magnitude. The wild type was able to recover and continue to grow after each hypoosmotic shock. However, for the E. coli double mutant the termination of the recovery was observed at 450 mM NaCl as well as the increased number of the dead cells at 650 mM NaCl. Furthermore, it was observed that all of the cells after the volume increase, except the wild type at 650 mM NaCl, were recovering their initial volume after a specific time. The hypoosmotic shock from 650 mM NaCl causes the excessive water loss in the wild type (below the initial value). By applying the shock of such magnitude on the ΔaqpZ mutant , it was established that the protein Aquaporin Z doesn’t partake in the excessive water loss. Likewise, such cells recover their volume gradually by potassium uptake.