In a recent study, researchers have estimated the energy required to produce bottled water, including the energy required to manufacture plastic, make the plastic into bottles, process the water, fill and seal the bottles, transport the bottles, and chill the bottles for use. Combining all the energy input totals for treatment and distribution, researchers found that producing bottled water requires between 5.6 and 10.2 million joules  of energy per liter, depending on transportation factors. That's up to 2, 000 times the energy required to produce tap water. To break down the energy requirements, researchers found that producing the plastic bottles and transporting the bottles greatly dominated  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 energy intensive 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. What's the main purpose of the passage?
To help consumers themselves make more environmentally sustainable choices. To advise the government to take severe measures to stop producing bottled water. To urge the consumers to drink tap water instead of bottled water for the sake of the earth. To try the best to find ways to produce bottled water cheaply and quickly for the companies.