No, "acre-feet" is an actual measure of large volumes of water.
ADDED IN EDIT:
One acre-foot is 1233481.84 litres. That's 325851.429 US gallons, or 271327.96 imperial gallons.
ADDED IN EDIT:
One acre-foot is 1233481.84 litres. That's 325851.429 US gallons, or 271327.96 imperial gallons.