Tap water requires a whole lot less energy than bottled water. No big surprise there. But within the world of bottled water, modes of transportation and distance can cause one bottle's energy footprint to be much bigger than another's.

Pacific Institute researchers Peter Gleick and Heather Cooley looked at the amount of energy consumed by the typical bottle of water from production to refrigeration, and wrote about their findings in Environmental Research Letters.

Starting off comparing tap and bottled water, it's no contest which uses less energy. Tap water needs only treatment and distribution, using about 0.005 million joules of energy per liter. Bottled water includes water that needs to be processed, and bottles that need to be manufactured, cleaned, filled, sealed, labeled, transported and refrigerated, consuming from 5.6-10.2 million joules of energy per liter.

The main factor that affects the total energy consumption per liter is transportation. The researchers looked at three types of bottled water, and how much energy it takes to get them to Los Angeles.

In the transportation energy efficiency hierarchy, rail is the most efficient, followed by cargo ships, heavy trucks, medium trucks and air cargo. But distance is a big factor, too.

Purified water (municipal water that's been treated) distributed by truck locally in LA uses about 1.4 million joules per liter. Spring water (a regulatory term that means the water came from an underground spring) sent by ship from Fiji to LA and then delivered by truck uses 4 million joules per liter. Spring water trucked from French springs to sea ports, shipped to the East Coast, then sent by train to LA, then delivered by truck uses 5.8 million joules per liter.

That may help an inhabitant of LA make a more informed choice when they buy bottled water (you know, when they don't have any access at all to tap water). But it provides only slight guidance to someone living in New York, or in the middle of the country. The best bet seems to be, when you can't go with water from the tap, go with local purified water.

Drinking water - CC license by rich115; Handing water - CC license by Ed Yourdon