Rapid intraperitoneal water injection induces acute hyponatremia that creates an osmotic gradient driving for water entry into the brain, leading to subsequent cytotoxic edema. Aquaporin-4 (AQP4) is a most abundant water channel in central nervous system and expresses mainly in astrocyte end-feet. However, it is still controversial that how AQP4 regulates water kinetics during cerebral edema due to the lack of experimental techniques for the observation of water distribution. We established T2-weighted indirect magnetic resonance imaging (MRI) with O¹⁷-labeled water to evaluate cerebral water kinetics during edema formation in wild type and AQP4-knock out mice. We scanned coronal sections of brain along the rostral and caudal directions using 7 tesla MRI up to 40 min after the bolus injection of distilled water equal to 10% of body weight. After intraperitoneal injection of O¹⁷-labeled water, O¹⁷ concentrations in cerebral cortex, cerebellum, and lateral ventricle rapidly increased and peaked out in about 10 minutes. Peak concentrations and the time of peak concentration of O¹⁷ in WT and AQP4-KO mice were comparable respectively in each brain regions. On the other hand, the O¹⁷ elimination half-life in AQP4 KO mice was longer than that in WT mice. These results suggest that AQP4 facilitates water permeability and excretion during edema formation, which probably exacerbates the cytotoxic edema.