Although the sports drink market is still dominated by heavyweights such as Gatorade and Powerade, beverages like Aquafina Essentials are rapidly becoming a popular alternative for the physically fit.

Sold by PepsiCo Inc., Aquafina Essentials is one of the latest offerings in sports drinks: “fitness water” or “enhanced water.”

Sales are skyrocketing despite a lukewarm reception from sports nutrition experts, who say the products are little more than flavored water with vitamins or herbs.

“You could probably get the same benefit from drinking Kool-Aid,” said Barbara Bushman, a sports nutrition expert at Southwest Missouri State University and spokeswoman for the American College of Sports Medicine.

Enhanced water, which tastes like a diluted fruit drink, hit the market in 2000 with the introduction of Glaceau Vitaminwater.

Energy Brands Inc., which makes Glaceau, wanted to offer a healthful, low-calorie alternative to sports drinks or soda pop, said Carol Dollard, the firm’s senior vice president of operations and technology. Energy Brands also markets Red Bull energy drink.

It also wanted to create a sports drink for a different group of consumers: those who exercise regularly and lead on-the-go lifestyles, but aren’t necessarily superathletes, Dollard said. Gatorade and other drinks often are high in calories and contain salt, electrolytes and other nutrients intended to help people recover from heavy workouts.

Glaceau, which comes in 14 flavors, has tripled its sales each year, and is attracting competitors. Reebok has jumped into the water business, selling a line of flavored and unflavored enriched waters. Propel Enhanced Water, introduced by Gatorade in 2002, has posted more than $100 million in sales.

Pepsi’s Aquafina Essentials line offers several nutrient-fortified versions of its popular bottled water brand.

While sales figures show that consumers are enthusiastic about the new drinks, nutrition experts generally are not.

Many believe that the drinks are an expensive form of sweetened water.

Most enhanced water costs $1 to $2 a bottle, less when bought in six-packs.

“This is really about where you choose to spend your money,” said Carrie Peterson, a University of Minnesota sports nutrition expert who is a consultant to Twin Cities professional sports teams. “For most people who work out less than 60 minutes (a day), good old tap water is just fine.”