The relevance of deionized water as a control treatment in vase life experiments and the effects of major tap water components on cut flower water balance were investigated. Chrysanthemum (Dendranthema x grandiflorum Tzvelev cv. Cassa) was used in all experiments. Deionized water gave a sharp decrease in fresh weight of the cut flowers after 1–3 days. This decrease was absent in tap water. After 4 days in deionized water, hydraulic resistance in the basal part of the stem was ∼50 times the value of fresh cut flowers and seven times the value in tap water. Change in fresh weight during vase life in a solution containing combinations of CaCl2, NaHCO3 and Cu2+ at concentrations commonly present in tap water was similar to that in tap water. However, none of the minerals tested by themselves gave fresh weight results similar to those from using tap water. In the combined solution, hydraulic resistance in the basal part of the stem after 4 days was comparable to that in tap water. A minimal amount of Cu2+ (>0.30 mg·l−1) enhanced fresh weight, probably by reducing bacterial growth in the cut open vessels. Calcium chloride (>0.7 mM) delayed the increase in hydraulic resistance in the stem (not including the basal 3 cm) compared to deionized water, and at a high concentration (10.7 mM), substantially decreased the transpiration rate. Sodium bicarbonate (1.5 mM) neither affected hydraulic resistance nor transpiration rate, but positively influenced fresh weight change during vase life when combined with CuSO4 and as compared to deionized water. Results strongly question the appropriateness of deionized water as a control solution in vase life experiments.