Many models for calculating hydraulic conductivity assume that the pore size distribution of a medium can be uniquely derived from the water retention curve. We examine this assumption by comparing water retention curves from simulations of drainage and imbibition of a domain network model to curves derived solely from the input pore size distribution. We use domain networks rather than the more usual oil reservoir pore scale networks to account for features of soils not commonly found in oil reservoirs. Simulated drainage and imbibition curves are substantially different from the input curve due to (1) the presence of a threshold in both the simulated drainage and imbibition curves and (2) the presence of entrapped air during imbibition. Differences between the simulated and input curves increase or decrease depending upon the network size, the type of percolation mechanism considered for drainage and imbibition, the aspect ratio of the pores, and the coordination number of the medium. ¿ American Geophysical Union 1993