A hamburger takes 634 gallons (2400 liters) of water to make. That’s enough water to make more than six bathtubs overflow!
How can a 1/3rd lb. (150 gram) hamburger patty, special sauce, lettuce, tomato all on a sesame-seed bun take so much water to produce, you ask? Since you can’t squeeze that much water out of your hamburger, it’s reasonable you should ask. Today is World Water Day, so I’m going to take a look at this question myself.
Where Did This Number Come From?
The 634 gallon (2400 liter) figure for a hamburger comes from an accounting of its total water footprint over its entire life, as reported by Arjen Hoekstra and Ashok Chapagain, back in 2005. Published in a 2006 issue of Water Resource Management, you can still download a copy of their report (pdf) to review this figure (and others) in the original context.
How a Water Footprint Differs
Most numbers accounting for a society’s water use were originally based on its macroeconomic-scale production (i.e., the water use in country X for sector Y is Z billion m³/year). Water experts soon discovered a leak in quantifying water use in this manner: many goods are imported or exported from elsewhere which shifts water use patterns across national boundaries.
If you’re in Japan eating a hamburger, chances are that hamburger was imported from an American cattle ranch in Texas. The portion of Japanese freshwater involved in producing that hamburger might be significantly less than the amount of American freshwater used in raising that heifer to adulthood. Nowhere will this water be accounted for when you examine the ledger line, “Japan’s Agricultural Sector used X amount of water.”
The water footprint concept was proposed in 2002 as a parallel to the ecological footprint concept introduced in the 1990s. It measures water use based on society’s consumption of goods and services requiring freshwater to provide. This plugs the leak caused by international trade. Although one country may be more efficient in its domestic water use (adopting water conservation practices, improved irrigation techniques, building water-saving technologies into its infrastructure), it may still be a major drain on the global water supply if it consumes water-rich goods and services brought in from abroad.
Virtual Water as an Opportunity “Lost”
These water-rich goods and services can be measured as virtual water. Going back to my original illustration, you can’t get this water by squeezing your hamburger. Whenever you sacrifice one thing that you could have had to obtain another, economists refer to it as an opportunity cost. The hamburger you may be about to eat was produced at the opportunity cost of not having 634 gallons (2400 liters) of freshwater to produce something else. While it may not be real water to you, it was real water to someone in drought-stricken Texas.
Water Consumption by Beef Cattle
Hoekstra and Chapagain’s methodology for measuring the virtual water content (VWC) of beef cattle to produce a hamburger in cubic meters (m³) of water per ton involved adding up the VWC of the feed given to beef cattle over a typical 3-year lifetime, plus the drinking and service water the cattle consumed. While a ton of beef would make one massive hamburger, calculating the VWC per individual hamburger patty is simply a matter of division.
At slaughter, the authors assume one beef cow will produce an output of 440 lbs (200 kg) of boneless beef, which could then be subdivided to produce approximately 1320 one-third pound (150 g) beef patties. Different portions of this boneless beef are where you would get your Angus beef, ground chuck, flank and skirt steak and other cuts from, so there would be far fewer Angus beef burger patties produced than this number suggests. I won’t consider the complication of these beef cuts further, although I don’t know if the authors had. The inputs necessary to raise a beef cow over the course of its lifetime were estimated by the authors from agricultural sources to be:
- 2860 lbs (1300 kg) of grains such as oats, corn, dry peas, soybean meal, etc.
- 15840 lbs (7200 kg) of roughage such as pasture grass, dry hay, etc.
- 6340 gallons (24 m3) of drinking water
- 1850 gallons (7 m3) of servicing water
Note that beef cattle do not consume a constant amount of feed or water, but need increasing amounts as they grow into adulthood, at which time their intake levels-off. In another report, “Virtual Water Flows Between Nations in Relation to Trade in Livestock and Livestock Products” (2003) (pdf), Hoekstra and Chapagain developed their model taking these variable consumption factors into account.
Owing to livestock’s higher position in the food chain, the quantity of water needed to produce any beef product is going to be greater than that for vegetable-based foods.
Calculating Water for Your Hamburger
Here’s a simplified walk-through of a virtual water content calculation for a one-third pound hamburger in the United States with a slice of tomato (most quick-service restaurants only include a single tomato slice to reduce their costs), no cheese (that would make it a cheeseburger, after all) on a bun (which I am going to assume is equivalent to 2 slices of bread: top and bottom).
Before I begin, I don’t expect to obtain exactly 634 gallons (2400 liters), because that figure is for a generic 150 gram hamburger of indeterminate composition, based on a global average (in some countries the specific water cost of certain ingredients will be greater than in other countries). Another limitation in my calculation is that the authors have gone to great lengths to take into account all fractional value uses of the livestock (boneless beef, offals, semen, etc) by it’s weight, which I’m not doing in this example. I encourage everyone to review their livestock report (pdf) to see details which I can only treat here in a superficial sense, if at all.
Slice of Tomato
Hoekstra and Chapagain give the VWC for a 2.5 oz. (70 gram) tomato as being 3.4 gallons (13 liters), so a slice that is one-tenth of a whole tomato would be one-third of a gallon in virtual water.
A 1 oz. (30 gram) slice of bread has a VWC calculated by Hoekstra and Chapagain of 10.6 gallons (40 liters), so the two halves of your hamburger bun would take approximately 21.2 gallons. If that sounds like a lot, consider that the bun may have sesame seeds on it.
Here’s the Beef
As for a pound (0.45 kg) of beef, given the inputs necessary to raise an average beef cow over its lifetime given above, that pound of beef required 6.5 lbs. of grains, 36 lbs. of roughage, and 41 gallons of water (drinking and service) to produce.
I will compute these figures from summary values given on page 1 in Appendix IXb of the “Virtual Water Flows Between Nations in Relation to Trade in Livestock and Livestock Products” (pdf) report. The authors there have broken-down the feed of beef cattle (based on Tables 3.5 and 3.6 within that report) in terms of how many tons of each sort of grain and roughage one beef cow consumes in a year drawn from USDA and Statistics Canada sources. They next multiply these figures by the specific water demand (SWD) requirements for each type of crop used as feed. The source of SWD measurements was a report by Hoekstra and Hung in “A Quantification of Virtual Water Flows Between Nations in Relation to International Crop Trade” (2002) (pdf). Some of these numbers are staggering, and at first glance I was surprised at the volume of water. Its weight was many times the weight of plant biomass.
Using the aggregates for the “Grains” and “Forage” (roughage) categories over 3 years, these numbers come out to 1896 m³ of specific water for grains plus 3321 m³ of specific water for roughage consumed in raising an average 1200 lb. beef cow in an industrial farming system, which produces 440 lbs. of boneless beef usable for the hamburger patty under consideration.
One difficulty for me in matching the authors’ calculation is that their figure takes into account all fractional uses of the beef cow. There is some other value in secondary products produced from the other 760 lbs of animal not going into your hamburger patty. All of these pounds are not created equal. In light of this limitation, I’m going to divide the specific water demand for grains and roughage by 1200 (instead of 440 or any interpolated figure for which I can’t give an explanation) to get a per-pound figure. Using this divisor, I find the VWCgrains required by 1 pound of beef is 417 gallons, and the VWCroughage required by 1 pound of beef is 731 gallons.
For 1 pound of hamburger, the calculation is 417 gal. (6.5 lbs. grains) + 731 gal. (36 lbs. roughage) + 41 gal. (drinking and service water) = 1189 gallons.
For the one-third pound of hamburger patty that is the subject of my example, this works out to be 396.3 gallons.
Finding the Total VWC
I sum each virtual water content figure together to obtain a total for the entire hamburger. This comes to a VWChamburger of 396.3 gal (the burger) + 0.3 gal (tomato slice) + 21.2 gal (the bun) = 417.8 gallons.
My 418 gallon (1582 liters) hamburger isn’t quite as large as Hoekstra and Chapagain (2006) calculated. I’ll remind you that it depends on where you buy your hamburger, how it has been made and with what ingredients, and several simplifications in my calculation compared to theirs. It’s plausible that their hamburger includes lettuce and onions. When I watched the World Water Day promotional video that cited this number, I tried to find the actual worked-out calculation, but couldn’t find one.
Anytime somebody quotes you a statistic like 2400-liters of water to produce a hamburger, you should research how it was determined. After having done so myself, I’m satisfied it’s a fair estimation. The lesson here isn’t that my figures came out differently, but that everybody should understand how much we depend on water.
On this World Water Day, we should all enlighten ourselves on the water we consume just in the food we eat everyday. Without water security, there can be no food security.