These days you can buy water with almost anything added - protein, vitamins, calcium, herbs, electrolytes, even chocolate! Manufacturers seem to think - apparently with good reason - that consumers want water to deliver more than mere hydration and are willing to pay a premium for enhanced products.
Reportedly, the thinking behind all these new products is that since so many consumers are in the habit of toting a bottle of water around all day, why not add stuff to it to make it (theoretically) healthier, tastier and more profitable? While researching this subject, I found a Consumer Reports article quoting a Pepsi spokesperson who said that consumers want water that "multitasks" and a Kellogg's marketing exec who said that dieters are interested in "easy, portable ways to add more protein and fiber to their diets."
While I see a limited role for vitamin waters (for people who can't swallow pills), I'm not impressed with those currently available. Most give you extra calories and additives that you don't need. Some vitamin waters (or "fitness" water, another product category) contain caffeine. Others contain artificial sweeteners. 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 a few vitamins and minerals, not all that a good supplement would deliver. You might have to drink multiple bottles of vitamin water to get your daily requirement for, say, folic acid. Conversely, some products may contain too much of a particular vitamin - potentially a problem if you drink more than one bottle a day, or consume other fortified products.
As far as protein waters are concerned, I think they're gimmicky and overpriced. The best way to get your needed nutrients is from the food you eat, particularly fruits and vegetables. You need only 10 to 20 percent of calories from protein each day. There's no advantage to consuming more than that. I recommend emphasizing the less-concentrated protein in plants, such as beans, whole grains, vegetables, and fruits such as avocadoes. All of these "multitask" better than any type of enhanced water: plant proteins come packaged with fiber, carbohydrates, healthful fats and phytochemicals that protect against disease.
Let water be water.
Andrew Weil, M.D.