The water exchange process on [(CO)(3)Re(H2O)(3)](+) (1) was kinetically investigated by O-17 NMR. The acidity dependence of the observed rate constant k(obs) was analyzed with a two pathways model in which k(ex) (k(ex)(298) = (6.3 +/- 0.1) x 10(-3) s(-1)) and k(OH) (k(OH)(298)= 27 +/- 1 s(-1)) denote the water exchange rate constants on 1 and on the monohydroxo species [(CO)(3)Re-1(H2O)(2)(OH)], respectively. The kinetic contribution of the basic form was proved to be significant only at [H+] < 3 x 10(-3) M. Above this limiting [H+] concentration, kinetic investigations can be unambiguously conducted on the triaqua cation (1). The variable temperature study has led to the determination of the activation parameters DeltaH(ex)(double dagger) = 90 +/- 3 kJ mol(-1), DeltaS(ex)(double dagger) = +14 +/- 10 J K-1 mol(-1), the latter being indicative of a dissociative activation mode for the water exchange process. To support this assumption, water substitution reaction on 1 has been followed by O-17/H-1/C-13/F-19 NMR with ligands of various nucleophilicities (TFA, Br-, CH3CN, Hbipy(+), Hphen(+), DMS, TU). With unidentate ligands, except Br-, the mono-, bi-, and tricomplexes were formed by water substitution. With bidentate ligands, bipy and phen, the chelate complexes [(CO)(3)Re(H2O)(bipy)]CF3SO3 (2) and [(CO)(3)Re(H2O)(phen)](NO3)(0.5)(CF3SO3)(0.5).H2O (3) were isolated and X-ray characterized. For each ligand, the calculated interchange rate constants K'(i) (2.9 x 10(-3) (TFA) < K-i < 41.5 x 10(-3) (TU) s(-1)) were found in the same order as the water exchange rate constant k(ex), the S-donor ligands being slightly more reactive. This result is indicative of Id mechanism for water exchange and complex formation, since larger variations of K-i are expected for an associatively activated mechanism.