The need for inclusion higher-order correlation effects for adequate description of the excitation energies of the DNA bases became clear in the past few years. In particular, we demonstrated that the inclusion of triply excited configurations may play an important role in a proper description of the excitation energies of the cytosine molecule in realistic environment. In this paper we discuss the accuracies of excitation energies for the cystosine molecule in the gas phase and in the aqueous solution calculated with noniterative and iterative coupled-cluster methods that include the effect of triply excited configurations.