The residential consumption (in billions) in 2010 was approximately 52. Take half of that amount,26, to represent the amount of water used by households with efficient appliances and plumbing. Let W represent the amount of water these households would have used otherwise.
Set up a percent equation to solve for W. Remember, the saving were 35%, so subtract 35 from 100 to find the amount that would have been used.
The savings in billions of gallons were 40-26=14.
Easy Data interpretation solving process.