Definition - What does Acre-Foot mean?
An acre-foot is a measurement of volume for liquids (most commonly water). It is defined as the volume liquid required to cover an area of one (1) acre to a depth of one foot.
An acre-foot is equivalent to 43,560 cubic ft (ft3), 325,851 gallons (gal) or 1,233 cubic meters (m3)
Trenchlesspedia explains Acre-Foot
The acre-foot unit is most commonly used in the United States to provide volumetric measurements of large-scale water resources such as sewers, irrigation sources, reservoirs, dams, aqueducts, and canals. For sufficiently large quantities of water, volumes may be expressed as thousands of acre-feet, often abbreviated TAF.
Expected sewer volumes, expressed in acre-foot, give an indication of the size and complexity of the piping network required. This can be used in trenchless construction to estimate the cost of piping material and determine appropriate sewer pipe sizes.
In other countries, where metric units are more commonly used, these volumes may be expressed in liters or cubic meters.