Water Efficiency

Reevaluating the Acre-Foot

Shifting units of measure to better quantify demand

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It’s interesting to consider the origins of various units of measure. The acre, for example, once defined the area of land that a team of oxen could plow in a day. The Egyptian cubit, used in ancient architecture, represented the length of a man’s forearm, from the elbow to the tip of the middle finger. It became the basis for the British inch, foot, and yard.

Today water agencies in the western United States are reevaluating the relevance of the acre-foot, a unit of volumetric measure that may no longer accurately define consumers’ water needs.

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For decades, the acre-foot has served as a standard volumetric used by water agencies to calculate demand. One acre-foot of water—325,000 gallons—was considered an adequate supply to fulfill the indoor and outdoor needs of two households for one year. But today consumers require less water, thanks to conservation programs, water-efficient technologies, and public awareness campaigns. Therefore, many water agencies in the west believe that this unit of measure should be reconsidered and a more precise one proposed.

As western states pare down water usage, some feel that the unit of measurement should decrease in parallel. Water usage in Nevada has dropped in the past decade. Today, an acre-foot is enough to supply two Las Vegas households for about 15 months. In Arizona, where conservation and reuse programs have reduced consumer usage significantly, an acre-foot is sufficient for three households. And California’s household water usage has decreased as well.

“Average residential water use varies widely throughout California, depending on factors such as housing density, landscaping, water rates, and when development occurred,” explains Gary Pitzer for Water Deeply. “Based on a sampling of 18 water agencies across California, the state estimated that in 2016, in the midst of the drought, an acre-foot was enough water to supply 3.4 households.”

As conservation programs and water efficiency technologies reduce the amount of water required by consumers, is it important to modify the standards of measurement? Should there be a smaller unit of measure to accurately define the amount of water one household? What do you think that the new unit of measurement should be based upon? WE_bug_web

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  1. Great Idea!
    I think it should be based on a person per month. 1 bod is the amount of water a person uses per month and 1 hut is the amount of water a house used per month.

    By breaking down to monthly we get a more accurate use through out the year. Also using a bod allows for the discrepancy of house size.

  2. But an acre-foot is a measure of volume, not a measure of households or relative (temporal and geographical) efficiency. We assess the volumetric capacity of a reservoir by a measure of volume, then the water users and planners convert appropriately based on their metrics.

  3. I think the acre foot or cubic measurement is still the best measurement for water storage reservoirs, tanks, etc. These are typical and widely used world wide.

    As For Usage: Thousand gallons or cubic measurement should be used to measure water consumption per person. All water meters, as do compressed air, gas, and other liquids meters typically measure cubic volume passing through pipes. The data or meter scale is converted to appropriate units of liquid or gas measurement.

  4. I’m for Mr. Williams’ (comment above) method. Here in Humboldt County, we have plenty of water. I know this is not the case for most of the rest of the state, and indeed just about everywhere else in the intermountain West beyond the Pacific Northwest. My point is, just this past summer, the local Community Services District–that supplies water to those of us in their area–raised our rates. Growing up in a household of thoughtful conservatives (depression era parents), I have always been keenly aware of the amount of water I use, and the way in which I use it. Unlike those who use this resource profilagtely, I make a concerted effort to respect water. Nevertheless, I’m penalized by a rate hike because our society at large (and especially southern California to whom we send the greater percentage of our water for profit) uses it with senseless abandon. Measure properly, and make people pay for the water they use individually or by household. The infrastructure is already in place (metered), so let’s give credit where credit’s due! Enough of us who are informed and critically consider the value of our natural resources having to pay for the lazy, reckless behavior of those who apparently can’t be bothered to consider the ramifications of their excesses!

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