Exchange of cerebrospinal fluid (CSF) with interstitial fluid (ISF) is a recently elaborated pathway by which solutes are trafficked into and out of the brain. This pathway has been implicated as a clearance mechanism for proteins such as amyloid β and tau, prior to pathogenic aggregation, a process characteristic of several neurodegenerative diseases. The mechanisms responsible for CSF-ISF exchange are poorly understood but have been linked to the expression of the astrocytic water channel aquaporin-4 (AQP4). AQP4 is unique in that it exhibits a profound localization to the perivascular spaces at which CSF-ISF exchange occurs, and that pathological states, including aging, dramatically reduce this localization. The significance of this loss of localization for CSF-ISF exchange and neurodegenerative disease has not been articulated. Here, we use imaging and cellular based approaches to study the role of AQP4 and the astrocytic endfoot in CSF-ISF exchange and aggregating protein clearance.