An unlikely new environmental villain is making people think twice about the drawbacks of a common convenience – bottled water. Even in this season of sweat and outdoor activities, store-bought water seems like a bad choice to folks who want to reduce trash buried in landfills and reduce the amount of oil burned needlessly. Bottled water, it turns out, has a much bigger impact on the environment than most of us realized until recent attention was stirred up.

Because buyers don’t recover a cash deposit for returning water bottles, they often get tossed instead of recycled. And we do use a lot of them: Americans consume 38 billion single-serving containers of bottled water a year, sales figures show. In addition to all that garbage, making the bottles, shipping the water and keeping it cold adds to the oil-burning carbon emissions that cause global warming, It takes 1.5 million barrels of oil a year to make the plastic water bottles Americans use, according to the Earth Policy Institute in Washington. “More than 90 percent of the environmental impacts from a plastic bottle happen before the consumer opens it,” says a senior scientist at the Natural Resources Defense Council.

He and other crusaders note that tap water in most areas is just as pure and refreshing as Desani, Poland Springs, Aquafina, Deer Park or Evian. “This country has some of the best public water supplies in the world,” a New York Times editorial said this month. That fact led four big-city mayors this summer to urge residents of San Francisco, Salt Lake City, Minneapolis and New York to drink tap water instead of the store-bought kind. That helped spread a national dialogue about the issue.

Industry says: “Bottled water provides consumers with access to convenient, refreshing water that they can carry and drink throughout the day. Our industry also cares about the environment. That's why bottled water containers are 100 percent recyclable and account for less than 1 percent of our nation's waste stream.” -- Susan K. Neely, president/chief executive, American Beverage Association

Environmentalist says: “Through education and motivation you can get people to change their habits. It’s easy to fill a bottle of water [from the tap] and stick it in your backpack.” – Emily Lloyd, New York City environmental protection commissioner

What’s changing: Growing awareness may bring more plastic recycling bins in public places. Companies that make Brita water filters and Nalgene reusable beverage containers advertise the benefits of refilling personal water bottles from the tap.