An ink includes water, a pigment, and a copolymer, wherein the copolymer contains a structure unit represented by the following Chemical formula 1, where R1 represents a hydrogen atom or a methyl group, M1+ and M2+ each, independently represent monovalent cations, n and m each, independently represent 0 or integers of from 1 to 6 excluding a case where both are 0 and a structure unit represented by the following Chemical formula 2, where R2 represents a hydrogen atom or a methyl group, Y represents an alkylene group having 2 to 18 carbon atoms.