There could be hard times ahead for soft drink makers producing and selling bottled water. Though it's possible that the popularity of bottled water will continue to grow, there are a variety of forces that could cause people to reconsider their purchase of bottled water — in favor of old-fashioned tap water.

When the bottled water industry started, the product in the bottle generally was, in fact, pure spring water. Today, however, when giant soft-drink companies such as PepsiCo and Coca-Cola dominate the market, the liquid in the bottle is often municipal water — plain tap water — that's received additional filtration and treatment.

Aquafina, Pepsi's bottled water product, does not say on the bottle that the liquid inside is from a spring. But the label design features a mountain range with a sun just beyond the peaks and claims both "pure water" and "perfect taste."

Soon, the label will also specify that the water comes from a "public water source." A group called Corporate Accountability International has been pressing for more truth in labeling, and recently PepsiCo officials agreed to explain on the label that the water in the bottle originates from a public water source.

Across the country, larger cities are waging a campaign to promote municipal water over expensive bottled water. There's plenty of logic for such a move, especially considering the fact that an estimated 40 percent of bottled water comes from those same municipal water systems.

In San Francisco, the mayor banned the city from buying bottled water, and the mayor of Los Angeles followed suit. In Ann Arbor, Mich., the city will no longer allow commercially bottled water to be sold at city-sponsored events. Salt Lake City officials have directed department heads to eliminate bottled water.

In an apparently related move, the U.S. Conference of Mayors is working to promote the benefits of public water systems and the negative environmental impact of bottled water, from the manufacturing and disposing of the plastic bottles themselves to the energy costs of transporting the bottles.

The superiority of bottled water is increasingly being questioned. In several different taste tests, a few experts were able to identify some bottled water samples in a blind tasting with municipal tap water, but most consumers (and many food or beverage experts)cannot.

And when the price for bottled water is virtually a thousand times more expensive than tap water, some people are beginning to rethink their bottled water habit. Tap water, in many homes, is filtered and considered an alternative to bottled water.

A campaign titled "Think Outside the Bottle" is designed to encourage people to choose tap water over bottled water whenever possible.

For many people, that changing mind-set might begin once they realize that bottled water doesn't necessarily taste better and that it's quite expensive when compared with essentially free tap water. Beyond that, there is the cost and consumption of energy and the petroleum products required to make billions of plastic bottles and transport them around the country and the globe.

Certainly, bottled water is not bad. It just might be that it is not as good as, or better than, tap water when the big picture is considered.

Drinking water is healthy, whether it's pricey bottled water or old-fashioned tap water. But it's also healthy for people to reconsider all the pros and cons of bottled water.

If some major cities have their way, and if the environmental downsides of bottled water are considered, tap water might be on the verge of a comeback.