Epithelial cells of the choroid plexus contain the blood-CSF barrier and play a pivotal role in brain water homeostasis. Here, DCE-MRI was used to investigate choroid plexus water exchange in 25 older individuals. A marked non-linearity of blood and tissue R1 values was observed, indicating that water exchange departs the fast exchange limit at clinical blood contrast agent levels. Using a two-site model that explicitly incorporates water exchange between intra- and extraventricular compartments, a mean rate constant for ventricular water efflux, kio, of 0.26 ± 0.13 s-1 was obtained. Significant associations of kio with age and cognitive status were found.