Water uptake in diglycidyl ether of butanediol (DGEB) epoxy cured with 4,4'-diaminodiphenyl sulfone (DDS) was studied using UV reflection spectroscopy. There is a progressive shift to longer wavelength of approximately 13 nm for the DDS reflection peak at 338 nm upon exposure to water, apparently due to hydrogen bonding of water to DDS through the SO2 group. The fraction of hydrogen-bonded DDS through SO2 with water was estimated by spectral deconvolution, and subsequently the fraction of hydrogen-bonded water to DDS through SO2 was obtained. When the epoxy is saturated with water containing. 9 wt % of epoxy, the SO2 group in DDS is fully hydrogen bonded, while 32% of absorbed water is hydrogen bonded to the SO2 group of DDS. Since hydrogen bonding of water to the tertiary amino group of DDS does not show up in UV reflection spectra, the fractions of hydrogen-bonded water are smaller than the values published recently by NIR studies, which account for both types of hydrogen-bonded water.