This paper describes the development of a suction controlled flexible wall permeameter for the direct determination of the water permeability function in unsaturated soils. The new permeameter works with applied constant head or constant rate of flow, i.e., the common steady-state techniques. Total volume change of soil specimens during the test are monitored using a high resolution electronic scale. Numerical simulations were performed to evaluate the influence of factors such as flow velocity and matric suction distribution within the specimen and effects of sample height on such factors. Analyses of tests conducted on two tropical soil samples are used to evaluate conventional proposals for the determination of the water permeability function. It is shown that such proposals do not apply in the case of the materials tested and solutions to that are put forwards.