The equilibrium adsorption of water onto activated carbon is a frequently encountered phenomenon in the industrial operation of adsorbers. This situation highlights a need for a method of prediction of equilibrium adsorption of water onto activated carbon that can be applied to adsorber models. This study examines an existing method of prediction of water-carbon and water-organic-carbon adsorption equilibria, making necessary adaptations such that a new method is evolved, which is suitable for inclusion in an adsorber model.