We present a method for high resolution, high precision measurements of water content in vivo, validated by comparison of the values obtained in the same brains at 3T and 7T. Applications relevant to brain structure and function are illustrated. The cortical distribution of water content simultaneously reflects its complement, the macromolecular content of tissue. Furthermore, a 3D “long TR” single-scan mapping method with 3deg excitation angle is proposed at 7T and delivers results consistent with the 2D method. Structural scans reflecting quantitative properties of tissue can thus be obtained in a short (7min or less) measurement time.