Through CO2 and H2O co-adsorption, more adsorbed H2O leads to higher CO2 adsorption capacities at ambient CO2 concentrations, increasing working capacity. However, if enough H2O is present during the desorption step, the same effect can also significantly raise the CO2 adsorption capacity at the desorption conditions, decreasing working capacity. This complicated effect, plus the increased heat requirement and consequently longer desorption time during the desorption step if more H2O is adsorbed, explains the substantial impact on productivity, specific thermal energy, and specific electricity in a TVSA process. It is imperative to consider H2O adsorption when evaluating process performance using process modelling.