SummarySoil water studies involve physical quantities, units and symbols, and these are discussed in terms of the International System of Units (SI) and the soil physics terminology (1976) of the International Society of Soil Science.The author particularly examines(i)the relation of SI units to the familiar but superseded cgs units;(ii)the effect of the frame of reference on the expression of water potential and hydraulic conductivity;(iii)the different interpretation of hydraulic conductivity in soil physics and in biophysics; and(iv)methods of avoiding ambiguity in presenting data.