A water dispersion containing colorant-containing water-insoluble vinyl polymer particles, and a water-based ink containing the water dispersion. The water-insoluble vinyl polymer contains constitutional units of formulae (1) and (2): where R1 is a hydrogen atom or a methyl group; and R2 is a substituted or unsubstituted arylalkyl group or a substituted or unsubstituted aryl group; and where R3 is a hydrogen atom or a methyl group; R4O is an oxypropylene group; R5O is an oxyalkylene group having 2 or 4 carbon atoms; R6 is a hydrogen atom, an alkyl group or an unsubstituted or alkyl-substituted phenyl group; x is a number from 1 to 30; and y is a number from 0 to 30, and a weight ratio of the constitutional units of formula (1) to formula (2) in the polymer ranges from 1/2 to 10/1.