Rate constants for base-catalyzed, uncatalyzed, and acid-catalyzed additions of water to 50 compounds (aldehydes, ketones, esters, thioesters, and amides) have been calculated using Multidimensional Marcus Theory. For all of these reactions except hydroxide addition to reactive aldehydes a single average value of the intrinsic barrier (8.51 kcal/mol) can be used to give calculated values within 1 kcal/mol (root-mean-square error) of the observed values. For the addition of hydroxide to reactive aldehydes it is necessary to use an intrinsic barrier linearly related to the equilibrium constant for hydroxide addition. The work term in Marcus Theory is approximated by a detailed model of the solvation and statistical cost of bringing reactants together.