The water state in the CaSO4 solutions where concentrations ranged from 0.68-7.08 g/l was studied by the differential-scanning calorimetry. In the low-temperature range, 248.8 K, a peak was detected at the beginning of a CaSO4 concentration of 1.7 g/l. Its appearance could be attributed to an initial moment of the crystallization, that is, a formation of the CaSO4 nuclei. The resulting increase in the CaSO4 concentration (up to 4.7 g/l) promotes a growth of the low-temperature peak. The effect of the inhibitors on the water state in the CaSO4-containing solutions was examined to clarify the role played by these potential scalants. Solutes of different chemical natures were used as inhibitors. As the thermograms demonstrated, an addition of the inhibitors into the system tested did not influence the formation of the CaSO4 nuclei but it precluded the resulting growth of crystals. An increase in concentration of the inhibitors results in a decrease of low-temperature peak. This testifies to the slowing down of the formation process of the CaSO4 nuclei. Better results were established by the presence of polyacrylamide and carboxymethyl cellulose while those with the presence of PE-1 polyelectrolyte were somewhat worse. The use of polyacrylamide as an inhibitor has been shown to increase the retentivity of the OPAM-KN membrane up to 0.90.