Ligand exchange involves replacement of a water ligand ("coordinated water") with water in solution ("bulk water"). Often the process is represented using labeled water :
In the absence of isotopic labeling, the reaction is degenerate, meaning that the free energy change is zero.
Rates vary over many orders of magnitude. The main factor affecting rates is charge: highly charged metal aquo cations exchange their water more slowly than singly charged cations. Thus, the exchange rates for  and  differ by a factor of 10. Electron configuration is also a major factor, illustrated by the fact that the rates of water exchange for  and  differ by a factor of 10 also. Water exchange usually follows a dissociative substitution pathway, so the rate constants indicate first order reactions.