Acre-feet are often used to measure the amount of water used for irrigation in agriculture. In the United States, for example, farmers use an estimated 140 million acre-feet of water for irrigation each year. This is equivalent to the amount of water that would fill the Grand Canyon more than twice.
Acre-feet can also be used to measure the volume of water stored in reservoirs. In the United States, for example, the largest reservoir is Lake Mead, which has a capacity of 26.1 million acre-feet of water. This is equivalent to the amount of water that would flow over Niagara Falls for more than 10 years.
Acre-feet are a useful unit of measurement for water because they are easy to understand and visualize. They are also a convenient way to compare the amount of water used for different purposes or stored in different reservoirs.