Water was traditionally only "counted" if you pumped it out of a lake or aquifer. There was plenty of data on water people had paid for. Agriculture, for example, consumes 70% of the fresh water people pay for. But crops aren't watered solely by irrigation.
Based on his research into water management, engineering, and policy, Professor Hoekstra proposed a new paradigm that would allow all water use to be captured. Most human activites require one or more of the following types of water:
In the years since 2002, Professor Hoekstra has created a huge body of research in peer-reviewed publications. He has built a global scientific consensus on how water should be "counted," and what quantity of water is used for any of a vast number of human activities. I point this out since the common response folks have when I talk about water footprint is to question the numbers and definitions.
Most common people simply cannot believe their life activities require thousands of gallons of fresh water per week. And the vast majority of the fresh water we consume goes to produce our food. With the globalization of food, we may be completely unaware of the water consumed to put food on our table, or the impact our "extraction" of that water has on the local peoples.
In 2011 Professor Hoekstra and his colleagues produced two documents that allow us to compute the water consumed to produce our food on an individual level:
These scientific papers express the amount of green water, blue water, and grey water required to produce a quantity of, say, sugar or beef. Unfortunately for the average American, these data are in terms of cubic meters of water per metric ton of product. We don't "speak" metric, and we don't eat tons of anything. Even when the numbers are expressed as liters per kilogram of product, our eyes glaze over.
I've taken the data from Professor Hoekstra's 2011 reports and converted it to the number of gallons per ounce or gram of each product. For the next year, I'll be measuring the weight of what I eat, estimating the amount of "product," and compute the water it took to produce that food.