This is not a newly published paper, but I found it well worth summarizing here.
“Footprint” evaluations — ecological, carbon, or water — determine the amount of a resource needed to produce a unit of a good. This paper calculated the water footprints per ton and per cup of tea and coffee, as well as “virtual” water imports into the Netherlands for each beverage. I’ll only summarize the water footprint of coffee here, but the paper can be downloaded from the publications list at the Water Footprint Network.
The authors measured coffee crop water requirements in different parts of the world. Some regions must irrigate (e.g., Brazil) while others rely on rainfall. Water used in processing, which also varies by region, was then factored in. Much of the world’s coffee (especially arabica) is wet processed, requiring a water source such as a river or groundwater to ferment and wash the coffee prior to drying the beans.
The calculations also took into account the shrinking weight of the product throughout processing — e.g., fresh cherries to pulped cherries to hulled beans, etc.– in order to keep the metric (cubic meters of water per ton of coffee) consistent.
Because of all the variability, from annual crop water requirements (they used FAO estimates) to the number of grams of ground or instant coffee used to make a weak or strong cup, this whole operation is somewhat of an inexact science. However, the authors appeared meticulous in their choices and inclusiveness, and the results seem to at least give us a relative picture between regions and methods, if not numbers that are actually well in the ballpark.
As it turns out, there was little difference whether coffee was wet or dry processed. The water used in wet processing made up only 0.34% of water used to grow the coffee. The summary tables provided figures for wet processing only.
The main results summarized the cubic meters of water used per ton of coffee (for each step from fresh cherry to roasted) for 25 countries. The two countries with the highest totals were both robusta-producing nations: Togo (49341 m3/ton) and Ghana (47554). In fact, six of the top ten countries grew robusta either exclusively or in addition to arabica. The highest arabica-only country was Panama at 37660 m3/ton.
The average (weighted for world production) “virtual water content” was calculated at 20987 m3/ton. Lowest countries were Vietnam at 6054 and the U.S. (Hawaii and Puerto Rico, 9061). Other countries that grow primarily arabica which were ranked below-average were Ethiopia, Guatemala, Costa Rica, El Salvador, Bolivia, and Colombia.
Finally, the authors calculated that the “average” cup of coffee required around 140 liters of water; several variations were provided. The authors also estimated that if the price of coffee included the economic value of rainwater, it would increase about 20 cents per kilo. This cost increase does not include surface or groundwater used for processing or irrigation water, nor any environmental costs due to erosion or water pollution.
Coffee flotation in Chiriqui, Panama; photo by Darrin O’Brien, used with permission.
Chapagain, A., & Hoekstra, A. (2007). The water footprint of coffee and tea consumption in the Netherlands Ecological Economics, 64 (1), 109-118 DOI: 10.1016/j.ecolecon.2007.02.022