Which unit is used to describe large volumes of water for planning in Texas?

• A. Million acre-feet
• B. Acre-feet
• C. Billion gallons
• D. Thousand gallons

Answer: (A)

Understanding how water planners describe large volumes helps make sense of why this unit is used. The acre-foot is the standard volume for measuring water: the amount that would cover one acre to a depth of one foot. When Texas planners talk about regional supplies, reservoir storage, or multi-year yields, they express these volumes in millions of acre-feet. This scale fits the size of state and basin projects and makes it easy to compare planned supplies to storage capacities and drought reserves. For example, one million acre-feet equals about 325.9 billion gallons or roughly 1.23 cubic kilometers. A thousand gallons is far too small to describe reservoir or statewide planning, and while billions of gallons can describe large volumes, the acre-foot-based millions-of-acre-feet unit is the standard in Texas planning practice.