I'm skeptical about the vitamin waters currently available, but I do see a role for the concept. For the many people who can't take pills or don't like taking them, vitamin-infused water could be a satisfactory alternative.
From what I've learned of vitamin waters on the market today, however, I'm not impressed. Most give you extra calories and additives that you don't need. Some vitamin waters (or "fitness" water, another category of new products) contain caffeine. Others contain artificial sweeteners. And I haven't seen any evidence that the vitamins the waters claim to contain are there in sufficient quantity to meet nutritional needs. Some products contain only some vitamins and minerals, not all that you would expect from a good supplement. You might have to drink multiple bottles of vitamin water to get your daily requirement for, say, folic acid.
I also have questions about how manufacturers deliver oil-soluble vitamins, such as vitamin E, in water, and I wonder whether any of the vitamins remain stable in water for the shelf life of the product. Some, such as vitamin C, break down quickly after being exposed to air and might not be available to you unless you drink the whole bottle as soon as you open it.
Some manufacturers claim that vitamins are best absorbed in liquid form, but I know of no evidence to back up that idea. Getting your vitamins from bottled water also seems an unnecessary expense since the price is much higher than the cost of vitamin supplements. You are always better off getting your vitamins from your daily diet. For insurance, I recommend a good multivitamin/multimineral supplement. Given the cost of vitamin waters, I would imagine that their main benefits are to manufacturers' profit sheets.
Andrew Weil, M.D.