Thanks to Watering the Desert blog, I was pointed to an article in The Economist magazine that examines the concept of embedded water, previously discussed here in this blog. I'm glad that I wasn't completely credulous when reading the embedded water tables. From the friendly article:
On the back of the business card handed out by Tony Allan, the father of the [embedded water] concept, are the virtual-water values of various products: 70 litres for an apple, 1,000 for a litre of milk, 11,000 for a kilo of cotton, and so on. The value for a copy of The Economist is not included, but it has been calculated by the Green Press Initiative at about 11½ litres. That is little more than the 10 litres Mr Allan has for a single sheet of A4 paper, which suggests the exercise is inexact.
It can also be misleading. The oft-quoted figures of 2,400 litres for a hamburger and 15,500 for a kilo of beef lead to the conclusion that eating cows must be unconscionable. Yet some cows valued primarily for their milk may still end up on a plate, and others may be well suited to graze on grassland that would be useless for growing cash crops. In Africa a kilo of beef can be produced with as little as 146 litres of water. Moreover, virtual-water content will vary according to climate and agricultural practice. SABMiller uses 45 litres of water to make a litre of beer in the Czech Republic, but 155 litres in South Africa. In other words, the merit of virtual water is not to give precise figures but to alert people that they might be better off growing different crops, or moving their manufacturing to another country.