Fig. 1. An overview of the relationship between the different energy states of bound water in soil. The relaxation frequency, f_r, and the soil matric pressure, p_m, are plotted as a function of activation enthalpy, H*. The bar on top of the graph is an indication of the number of water layers bound to a soil particle. White represents no water and black a large amount of water layers. The bar at the bottom refers to the numbers of the list in the text