The effects of variation in heating temperature T (50–300°C), heating duration (20–60 min), and post-heating equilibration times (24–168 h at 20°C and 50% relative humidity) on the wettability, as measured by the Critical Surface Tension (CST) method, of 4 initially water repellent soils from Canada, Portugal, and the UK are reported. All soils show an increase in water repellency following heating at temperatures in the range of 50 to 150°C, followed by a considerable decline after heating to 200–250°C, and, except for one soil, the eradication of repellency after heating to 300°C. For two soils with a comparatively high organic carbon content and fine texture, water repellency levels were also affected by the length of the post-heating equilibration period.

The results demonstrate that (i) the common practice of heating samples to 105°C does not provide a viable standard procedure for the measurement of water repellency as it may alter repellency to different degrees, and (ii) where heat treatment is required, a post-heating equilibration time of 24 h is not necessarily sufficient for sample repellency levels to adjust to atmospheric laboratory conditions; therefore it is advisable to prolong equilibration to at least one week prior to measurement.