In Tables S1 to S3 are presented transient outflow measurements for suction steps 1, 4 and 11, carried out on a coarse volcanic substrate using the apparatus described in the paper "Two improvements to Gardner’s method of measuring the hydraulic conductivity of non-saturated media: accounting for impedance effects and non-constant imposed suction increment". Data are presented in the form of the change in water level [mm] in the outer (suction step 1 – Table S1) and inner tube (suction steps 4 and 11 – Tables S2 and S3), captured by means of the differential pressure transducer of high precision (0.1 mm). In Tables S4 and S5 are presented transient outflow measurements for the remolded poorly graded sand and undisturbed silty clay, respectively, published by Wayllace and Lu (2011). In case of both soils, only the first suction step is analyzed. Data are presented in the form of the change in mass of the water drained, which is monitored by means of the weight scale.