While studying changes in volumetric water content (VWC) of soilless culture (sand and tuff), the need for a quick and easy-to-operate moisture measurement device with accuracy better than ±0.01 has risen. Before full scale application, we performed some basic tests with the Fieldscout TDR 300 soil moisture meter to evaluate the dependency of the VWC measurements on the salinity of the medium. The TDR300 was used to measure VWC in (i) sand and tuff wetted by deionized water or a 0.02 M NaCl solution to different VWC levels, (ii) sand or tuff wetted by solutions of different salinities to a given VWC level, and (iii) aqueous solutions of different salinities. Medium salinity had a significant effect (up to 60%) on the VWC readings of the TDR 300. Our observations suggest that the technology used by the TDR 300 is similar to that of low frequency water content reflectometers.