The great thing about  this Swiss study on tap water vs. bottled water is that it takes a boring, commonsense intuition, and makes it interesting—just by providing a few numbers.

In this case, the intuition is that bottled water uses more energy—and thus releases more greenhouse gases—than plain old tap water.  The point is really obvious:  just think about the energy that’s required to manufacture bottles, and you can pretty easily guess that bottled water will be more energy-intensive than water from the tap. In fact, it’s so obvious, it almost seems pointless to do a study

water-climate chart, tap vs. bottled

But it turns out that there’s a very interesting point to be made:  the gap between bottled water and tap water is simply enormous.  Based on European data used in the Swiss study, water straight from the tap has about one half of one percent of the climate-warming impact of the most benign bottled water—and less than a thousandth of the overall environmental impact of the most energy-intensive bottled water.

In the chart to the left, I’m deliberately leaving the numbers vague.  The two bars actually average of a number of different figures—different drinking water systems, bottling options, and water temperatures.  So the numbers are a bit meaningless.  Still, they give a sense of the magnitude of the difference between bottled water and tap water.

In this case, the most important message isn’t simply that tap water is better—it’s the raw scale of the gap between tap water and bottled water.  Of course, bottled water doesn’t rank particularly high on the list of climate offenders, compared to cars and trucks, coal fired power plants, and the like. Still, if you’re a bottled-water drinker, and you’re looking for a quick and easy way to reduce your carbon footprint—and you’re lucky enough to live in a place with clean, tasty tap water—playing taps (ha!) for your bottled water is a pretty good place to start.