An ab initio QCISD/6-31+G* direct molecular dynamics (MD) study of the reaction of C+ with water has been performed and the mechanism of reaction examined. Principal products are isoformyl cation, HOC+, and H atom. There are two main channels, direct 'knock out' of a hydrogen, and via an intermediate, H2OC+, The intermediate is one not previously proposed in either experimental or theoretical studies of the reaction. Most product HOC+ molecules were found to be internally energetic enough to isomerize to formyl cation, HCO+.