This review describes the interaction of epoxy coatings with water, the kinetics of water uptake in epoxy resins, and the methods of studying the latter (gravimetric, IR (Infrared) and NMR (Nuclear magnetic resonance) spectroscopies). The analysis of experimental data requires using mathematical models which simulate the processes that occur during water uptake in a polymer matrix. This review classifies the numerous models applied for the study of water absorption into two large groups: Fickian and non-Fickian models. Fickian models involve the Fickian diffusion model and its development for the case of anomalous diffusion, as well as the models of Jacobs–Jones, Berens–Hopfenberg, and the time-varying diffusion coefficient model. The Carter–Kibler approach is provided as an example of a non-Fickian or Langmuir-type model. A critical analysis of the experimental methods is provided, including advantages and possible experimental errors. The methods used for processing experimental data are discussed as well as the effect of water on the exploitation properties and life cycle of epoxy coatings.