To test whether the weakening effect of added water in ductile deformation experiments on quartzite at high P-T conditions is associated with measurable changes in intragranular water content (cw) we determined Fourier transform infrared (FTIR) spectra of single grains (grain size 150--250 μm; IR spot size ~70 μm) in samples of Dongelberg quartzite experimentally deformed in a Griggs solid-medium deformation apparatus at a temperature of 800 ¿C, a confining pressure of ~1200 MPa, and a strain rate of ~10-7 s-1, both with and without ~0.4 wt % added water. The added water caused a weakening effect of a factor ≥9. Microstructural observations indicate that the dominant deformation mechanism in the weakened samples was solution-precipitation creep. The FTIR measurements showed that the starting material has a broad variation in cw as well as in the type of OH absorption. The cw of individual grains range from >200--2900 molar ppm H/Si (measurement resolution: 100--1000 molar ppm H/Si; standard error of average cw values 300--900 molar ppm H/Si). The experimentally deformed samples, whether deformed with or without added water, showed a broadly similar variation in cw with similar types of OH absorption. Relatively ''dry'' grains (3000 molar ppm H/Si) in samples deformed without added water. We were unable to demonstrate any significant changes in average cw after either of the treatments. Apparently, the water weakening effects seen in our experiments occurred without measurable changes in cw. ¿ American Geophysical Union 1994