Water footprint numbers are extrapolated using various sources, such as government agencies and industry associations, and are calculated by measuring each of the water inputs in a product's manufacturing process. The footprint of a pair of blue jeans, for example, is measured by calculating the amount of water used to grow enough cotton to make a pair of jeans (2,247 gallons) and to dilute the pesticides used in growing that amount of cotton to EPA standards (165 gallons), among other things.
Crunching the numbers for the amount of clothes I buy every year, it looks a lot like my friend's swimming pool. My entire closet is borderline Olympic.
My late resolution for the new year is to buy fewer clothes and to buy some items used. Underwear and socks are, of course, exempt from this strategy, but I have no problem shopping less and also shopping at Goodwill and other secondhand stores. In fact, I'd been doing that for the past year to save money and reduce clothing waste. My clothes' outrageous water footprint just reinforced it for me.
More conscious living and substitution, rather than sacrifice, are the prevailing ideas with the water footprint. It's one I'm trying, and it's one that's had an unusual upside. I had a hamburger from the Oinkster recently, and I enjoyed it a lot more since it is now an occasional treat rather than a weekly habit.