To break down the _energy_requirements,_researchers found that producing the plastic bottles and transporting the bottles greatly dominated(控制) the energy input. Although some companies are experimenting with producing lightweight bottles or using recycled materials, the researchers calculated that the manufacturing cost is about 4 million joules of energy per plastic bottle weighing 38 grams, and the cap weighing 2 grams.

　　“Our previous work had suggested that bottled water production was an energy­intensive process, but we were surprised to see the results, ” the researchers said.

　　Transportation costs vary depending on the distance and mode of transport, and both factors depend on the type of bottled water. There are two main kinds of bottled water in the US: “ _spring_water”， which comes from an underground spring; and “purified water”， which is city tap water that has received further treatment. For purified water distributed locally by truck within Los Angeles, the total transportation energy is about 1.4 million joules per liter. In the second situation, spring water shipped from Fiji (such as Fiji Spring Water) across the Pacific to Los Angeles, and then delivered locally by truck, requires about 4 million joules per liter for transportation. For the spring water, the transportation energy equaled (in the case of Fiji) the energy required to produce the bottle.

　　With this data, the researchers hope that future studies will have the ability to make specific estimates for different situations, and possibly find ways to cut energy costs.

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