Planets orbiting close to their host stars face a significant threat from photoevaporation, which can potentially erode their atmospheres to the point of complete removal. This atmospheric escape mechanism is thought to play a pivotal role in explaining the demographics of the observed exoplanet
population, potentially explaining the bimodal distribution of planets. While previous hydrodynamical research has primarily focused on hydrogen/helium atmospheres, the rapid advancement in atmospheric observations emphasises the pressing need to understand the resilience of more complex atmospheres. Consequently, the central research question guiding this thesis is: How does photoevaporation affect water-rich exoplanet atmospheres?