Green is hot. Green is roiling industries. Green is the new India—you know, the buzzword that has to be part of every business plan.

And this green wave will last, hmm, probably as long as most people managed to stay away from doughnuts when the anticarb fad hit.

Here in the United States, we take to environmentalism the way Eva Gabor took to farming. “Dahling, I love you, but give me Park Avenue.” The current green fad will have a nice little run, thanks to subprime-mortgage reverberations: Breakouts of environmentalism track with economic slowdowns, according to Gerald Celente, who runs the Trends Research Institute. We conserve when we must and then tell ourselves our sacrifice is helping to save the world. The human brain can twist anything.

The assault on bottled water fits right in. Sipping bottled water is suddenly more unsavory than wearing a chinchilla coat to your kid’s class play. San Francisco’s Gavin Newsom, the hippest mayor on the planet, banned city agencies from buying bottled water. Chichi restaurants around the country increasingly won’t serve it. The bottled-water industry is so alarmed, it apparently distributed talking points to the various water companies. “Let it be known that beverage containers are less than 1 percent of municipal waste,” says Nestlé Waters spokeswoman Jane Lazgin. Breck Speed, C.E.O. of Mountain Valley Spring, told the Arkansas Democrat-Gazette, “One-third of 1 percent of landfill waste may be attributed to bottled water.”

Certainly the argument against bottled water has merit. The stuff unnecessarily adds to your carbon footprint, and these days only an environmental nincompoop wants to do that. No one is certain how big a carbon footprint should be—you can calculate yours on carbonfootprint.com—and a few bottles of Evian probably won’t make much difference if you’re heating a house with a foyer the size of a grain silo. But still. Water bottles are made from polyethylene terephthalate, popularly known as PET. And PET is made from oil. The Earth Policy Institute calculates that to make the 29 billion PET water bottles used in the U.S. annually requires 17.6 million barrels of oil, or a year’s worth of fuel for 1 million vehicles. But if gas prices fall as a result of a drop in demand for PET, Americans will only buy more S.U.V.’s and suck up the difference.

Water in most parts of the U.S. is free, safe, and spiked with fluoride—from the tap. No bottles needed. The biggest bottled-water brand, Aquafina, is filtered tap water. Dasani, the second-biggest seller, comes from Brampton, Ontario, where factories also make cars and paint. It’s not like those PET bottles hold anything special.

So giving up bottled water is easy. It’s the lowest-hanging fruit of the green movement. See, there’s expensive green, like buying organic food or a Prius. Then there’s the conservation type of green—driving less, turning down the heat. With bottled water, no one has to give up much of anything. In fact, if times are tight and the bank’s foreclosing on your balloon mortgage, why buy something when you can get it for free and feel self-righteous?

Other industries watch and strategize. Green is catnip to the presidential candidates. They’ll pump the bellows for the next year. Companies are jumping in like penguins off a melting ice floe. Wal-Mart wants green products on its shelves. Tractormaker Caterpillar crows that it’s included in Dow Jones’ Sustainable World Index. Green tech is now the third-most-popular sector for venture capital, according to accounting firm KPMG.

Trend watchers such as 4.5 Productions are setting up businesses to tell other businesses to get into green stuff. “We soon came to realize that there are many companies that would like to introduce more eco-friendly or socially conscious aspects but didn’t really know where to start,” says Britt Allanson Bivens, a director at the New York-based company.

In the midst of any fad, the forces driving it seem real and powerful. Carbs make you fat? My word, you don’t want to be Dunkin’ Donuts or Macaroni Grill. Gas prices spike? Yikes! Everyone’s going to buy hybrids the size of golf carts. Chinese products kill your kids and pets? No one will ever buy “Made in China” again!

But now Dunkin’ Donuts plans to triple its outlets by 2020, S.U.V.’s have held steady at nearly a quarter of the new-car market, and last time anybody looked, the trade deficit with China was still growing.

Likewise, green will waver. Most of us get global warming. We’ve seen An Inconvenient Truth, or at least Happy Feet. We know we’re causing a mess. But global warming has a major marketing problem: It doesn’t have an immediate, tangible effect on our daily lives, and the only way we can do something about it is to give things up. Americans don’t like to give things up.

So green is “a trend driven more by economic survival—to make ends meet, to boost profits, and to assuage guilt—than by intellectual pursuit,” says a ­report by trend watcher Celente. “When money flows, the trend to buy big and spend large [pushes] enviro-care from the public’s mind.”

Right. So let’s meet in 20 years at what will then be your tropical beach house in Saskatoon. What the heck—pack lots of bottled water.