An acre foot of water equals about 326,000 gallons, or enough water to cover an acre of land 1-foot deep.

To put it another way, an acre foot of water is enough to flood a football field 1-foot deep (a football field is roughly an acre in size).

An acre foot of water is a common way to measure water volume and use. In California, an acre foot, or 326,000 gallons, can typically meet the annual indoor and outdoor needs of two average households. But, in more recent years, an acre foot began serving even more households.

Other common measurements involving acre feet include:

• The federal Central Valley Project delivers about 7 million acre-feet of water in a normal year – about 20 percent of the state’s developed water.
• The State Water Project delivers about 3 million acre-feet of water in an average year, with about 70 percent going to municipal and industrial use and 30 percent to agricultural uses.
• California’s flood management reservoirs provide more than 5 million acre-feet of seasonally reserved flood management storage. This amount would cover the entire state in about one-half inch.

Elsewhere, the highly contested Colorado River allocations are based on an average annual flow of 15 million acre-feet, every drop of which is fully apportioned. The water is used primarily for irrigation, power generation, and urban supplies.

The Colorado River is at the center of one of the oldest and most complicated water allocations battles regarding water allocations in the West. The river and its tributaries supply water to seven states (California, New Mexico, Colorado, Utah, Wyoming, Nevada, Arizona), Mexico, and American Indian tribes.