Water is known to play a key role in the solubility switching reaction of novolac-diazonaphthoquinone photoresists and certain chemically amplified resists. In order to quantitatively study these effects, an environmental chamber was built in which the % RH could be controlled while the extent of acid catalyzed deprotection was monitored during the post exposure bake by reflectance FTIR spectroscopy. The extent of acid catalyzed deprotection of tBOC, KRS-XE, UV6, and a tBOC-poly(hydroxystyrene) copolymer have been measured as a function of time over a range of 0-60 % RH. For tBOC, the deprotection reaction rate was found to slow considerably as the %RH was increased. Also, the relative film shrinkage varied considerably with varying % RH. Several possible mechanisms for the dependence of the reaction rate and thickness loss on % RH were investigated. For KRS-XE, the deprotection reaction kinetics were found to increase as the % RH was increased, which was an expected trend. For UV6 and the tBOC-PHOST copolymer, no change in deprotection reaction rate was observed with changes in %RH.