Free is an appealing price.

Playing to economic concerns may be a better bet than playing to environmental consciousness. After all, the almighty buck, not fear of the ecological havoc wreaked by plastic, is the real motivation behind Americans' renewed interest in tap water. Many consumers can no longer justify spending money on something they can get for relatively no cost from their faucet.

According to MSNBC, Americans spent $16.9 billion on bottled water in 2007, a 12% increase from 2006. This may not seem like a red flag, but it was the smallest rate of growth since the early 1990s. Having grown accustomed to the taste of bottled water, however, many Americans are turning to more cost-effective at-home purification systems. The tap movement has filled the profit pools of Brita and Procter & Gamble, (PG) maker of Pur.

In the past year, many brands of bottled water – among others, Poland Spring and Deer Park -- have made changes, introducing bottles that use 30% less plastic. But this reduction hasn't lowered prices, only profits.

In hot pursuit of hydration, tap may put a cap on bottled water.