I have had vitamin water before from the brand, Vitamin Water. Usually they contain water soluble vitamins that cannot produce toxicity. The B12 they contain is a great supplement for us veg*ns.
My suggestion: vitamin enhanced water is okay to drink, but you don't want it to replace water consumption. The sugar some brands use metabolize quickly and will leave you with blood sugar fluctuations if you drink it on a constant basis.
I like to enjoy sports beverages in this manner: during my aerobic or anaerobic exercise(s), I drink nothing but water. Once I am finished and my muscles are in dire need of fuel, I drink a high glycemic beverage such as Gatorade to quickly refuel my muscles with precious nutrients. Then I'll follow that with carbohydrates to supply my body with a steady flow of fuel.