The objective of the study is the calculation of the maximum absolute and relative measurement errors of the water conductivity coefficient determined by the instantaneous profiles method in the soil water potential range from 9.81 to 981 hPa. The analysis included average values of water conductivity coefficients from measurements on 415 soil samples for water potential values of 9.81, 31, 98.1, 156, 310, 490.5 and about 981 hPa. The measurement results were divided into classes according to selected physical properties of soil solid phase. It was found that the absolute measurement error of soil water conductivity coefficient by instantaneous profiles method originates mainly from reflectometric water content measurements. In the soil water potential range from saturation to field capacity the maximum relative error of soil water conductivity coefficient does not exceed 10% for a majority of the investigated soils. This range of soil water potential values is the most important to plants because water is easily accessible and the majority of hydrological research concentrates in the range. For the soil water potential close to the wilting point the maximum relative measurement error is about 50% (depending on the soil group). Its value results from low values of the measured water conductivity coefficients. However, in this measurement range water is not accessible for most of the plants and the effect of making a big measurement error does not influence the evaluation of the water flux in the soil profile.