It's useless and bad for you. As far as pH levels go, Vitamin Water (like most bottled waters) is acidic and not ideal for drinking (you want water with a pH of 7.5 to 8.5). For those of you interested in oxidation, just about all bottled waters have high levels of oxidation. I've personally tested several using an ORP (oxidation reduction potential) meter.
Waters treated with reverse osmosis (such as Aquafina or Dasani) are the worst, with ORP values as high as +800mV. You will very rarely find bottled liquids with negative ORP values (meaning it's an antioxidant), as oxidation increases the longer the product sits on the shelf or is exposed to light.
The best bottled water to drink is usually spring water like Arrowhead. They usually have neutral pH levels and a lower level of oxidation.
There are, however, ionization machines that will clean your tap water and ionize it. I've seen ORP levels as low as -1600mV in the water from these things. Not only that but hydrogen as an antioxidant is probably the best thing you can put in your body. The only problem is that these machines cost a fucking shitload of money. I simply can't justify spending 4,000 bucks on water.