In additional to summarizing these findings, Illif describes the key role that the astroglial water channel aquaporin-4 (AQP4) plays in perivascular glymphatic exchange and amyloid beta clearance, and the effect that loss of perivascular AQP4 localization in the aging and injured brain plays in the development of Alzheimer’s disease-related pathology. Here, AQP4 is linked to Alzheimer disease.