Why doesn't the TDR meter or WaterScout sensor read 100% Volumetric Water Content when immersed in water?

The calibration equations were developed in mineral soils in conditions varying from dry to saturated soil. This results in a range of about 0 to 50% water content. The relation does not apply
when measurements are taken in water. The nature of the calibration equation is such that the probe (or sensor) gives values less than 100% when in water.