The proton NMR chemical shift has been measured for water from 25 to 600 degrees C and from 1 to 400 bar, conditions extending well beyond the critical point. Dilute solutes were employed as chemical shift references to avoid the effect of the varying magnetic susceptibility. The large changes in chemical shift (4.1 ppm) are interpreted as changes in the hydrogen bond network, because al! other intermolecular interactions are known to result in much smaller effects. Using a linear relation between chemical shift and the mean number of hydrogen, bonds, the NMR results show there are still 29% as many hydrogen bonds at 400 degrees C and 400 bar (rho = 0.52 g/cm(3)) as for room temperature water, The present results are compared to other measurements and calculations.