How many Big Macs are in your water bottle?

Sustainability

Quick answer: there are 1.3 Big Macs in a bottle of water.
Now we have some explaining to do! Read on…

It was estimated that U.S. consumers purchased over 33 billion liters of bottled water in 2007 (Cooley & Gleick, 2009). The production of all that bottled water included:

  • making the plastic bottles,
  • processing the water,
  • bottling the water,
  • labeling the bottles,
  • transporting the bottles,
  • and chilling the water before drinking.

water_bigmacAll of these processes require energy, which means there is a significant amount of embodied energy in bottled water. But how can we conceptualize that energy?

One way that consumers think about energy is calories; food calories. It’s fairly well-known , for example, that a “standard” diet is about 2000 calories. So we thought it would be interesting to use food calories to evaluate the embodied energy in a bottle of water. (Especially since it is well known that water itself has zero food calories!)

Taking it a step further, let’s compare the energy required to produce bottled water and the amount of food energy contained within a Big Mac from McDonald’s. This is the frame for our question; how many Big Macs are your water bottle?

According to a paper written by Cooley & Gleick in 2009, the total energy required to produce a bottle of water is between 5.6 and 10.2 MJ(th) per liter. For our analysis we will use the small end of that range: 5,600,000 Joules per liter of bottled water.

According to the Mc Donald’s website, there are 530 food calories in a Big Mac (Mc Donald’s, 2010-2014).

Although nutritional facts for food products are written in calories, they are actually kilocalories (kcal) in scientific/engineering terms. So the Big Mac has 530,000 “science” calories.

The conversion for “science” calories to Joules is 4.184 Joules per calorie, so we can calculate the Joules of energy stored in a Big Mac:

530,000\text{ calories}\times\dfrac{4.184\text{ Joules}}{1\text{ calorie}}=2,220,000\text{ Joules}

Now we compare this to the amount of energy that goes into producing bottled water –

\dfrac{\dfrac{5,600,000 \text{ Joules}}{1\text{ liter of bottled water}}}{\dfrac{2,220,000\text{ Joules}}{\text{Big Mac}}}=2.52\text{ Big Macs per liter of bottled water}

This is in terms of liters of bottled water; however, a typical bottle is only about half a liter. Dividing 2.53 by two yields about 1.26 Big Macs per one half liter bottle of water. We’re justified in rounding a bit further, so we can say

1 half-liter bottle of water = 1.3 Big Macs
(in terms of embodied energy vs. food energy)

Next time you think about buying bottled water, I hope you consider the energy implications; feel free to use “Big Mac Units” while you ponder.

What we have not done here is evaluate the embodied energy in the Big Mac. That will have to be the subject of a future post.

 

References

Cooley, H.S. & Gleick, P. H. (2009). Energy implications of bottled water. Environmental Research Letters.

Mc Donald’s. (2010-2014). Retrieved from Big Mac: http://www.mcdonalds.com/us/en/food/product_nutrition.burgerssandwiches.5.big-mac.html

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