How much water is added to increase acidity?

Consider 1.0 L of a 1.0 x 10–4 M solution of a certain acid HA that has a Ka value of 1.0 x 10–4. How much water was added or removed (by evaporation) so that a solution remains in which 25% of HA is dissociated at equilibrium? (ume that HA is non-volatile.)