The Brooks and Corey equation is a well known empirical model for the soil water retention curve. This model contains four constants: porosity, residual water content, air entry value, and pore-size distribution index. More physically-based models for the soil water retention curve have been proposed based on fractal geometry. However, these models generally require the following unreasonable assumptions: (i) porosity is unity, and (ii) complete drainage of all pores according to the Young-Laplace equation. An equation is derived for random mass prefractals that relaxes these assumptions, allowing for fractional porosities, and partial drainage due to incomplete pore connectivity and/or the presence of surrounding smaller pores. The resulting expression is identical in form to the Brooks and Corey model and contains four fractal parameters that can be related to the empirical Brooks and Corey constants. Inverse estimates of these parameters are obtained by fitting the new equation to previously published water retention data for a wide range of natural and simulated random porous media.