Types of amidinium-water-base interactions. Bridging waters in furamidine (A, B), CGP40215A (C, D), berenil (E, F), DAPI (G, H), sandwiching water of DB921 (I, J), and a mix of both types with DB819 (K, L). Water molecules are shown as white spheres, ligands and interacting nucleotides as tubes, and other nucleotides as stick representations.