Global Reporting Initiative+Total water withdrawals, GRI 303-3-a (formerly G4-EN8-a)+Starbucks Corporation+2011+Discussion

p8.

20.11gal is water use per square foot per month. Per year amount is 241.32gal(0.913495572m3) per square foot. However, total square feet is unknown. Therefore, total water withdrawal amount is unknown. 

The report states that the total water use in 2011 is 17.6% decrease from 2008.