# cost per lifetime acre-feet saved

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#### Trimple

##### Member
Dear all,

I am trying to figure out the meaning of "utility cost per lifetime acre-feet saved"
described in a chart demonstrating the effectiveness of water conservation measures.

The source is "Smart Savings Water Conservation" by Western Resource Advocates
(Chart on page 4, Executive summary)

One related paragraph mentions,
"We gathered information from various utilities across the western United States, in
addition to Sydney, Australia, to highlight the cost per acre-feet (AF) of water saved
throughout the life span of numerous conservation measures. Table 1 summarizes
what we found."

For example, the first line of the chart mentions:
Conservation measure: Toilet retrofit
Estimated life span: 25 years
Utility cost per lifetime AF saved: \$75

What saving is \$75? The cost saved over 25 years, for each AF saved?
But \$75 seems to low for that...

Trimple

• #### papakapp

##### Senior Member
I think you are reading it correctly.
And, I would be quite surprised if a low-flush toilet saved more than 75 bucks over 25 years. My water bill is about 35 bucks a month, and the percentage of the water I pay for that flows through my toilet is maybe .0025%. So I would not expect a huge savings.

But even with all that, the acre-feet saved is completely redundant in your context as far as I can tell.

Simply saying "Lifetime utility cost saved" would mean the exact same thing and be much less confusing.

#### Thomas Veil

##### Senior Member
utility cost per lifetime acre-feet saved = (Cost of the conservation measure) divided by ((Total acre feet of water that would be used without the conservation measure) minus (Total acre feet of water that would be consumed with the conservation method))

Basically, the conservation method is saving water, but it costs money. So the question is: how much is this extra water costing? If you go to a gas station, the cost of the gas (at least in the US) will be given as "dollars per gallon". Similarly, the price of water is often given as "dollars per acre-feet". It doesn't make sense to just give the dollar amount; the dollar amount is divided by the amount of water saved so that the costs can be meaningfully compared

"And, I would be quite surprised if a low-flush toilet saved more than 75 bucks over 25 years."
That's not what the figure means.

"But even with all that, the acre-feet saved is completely redundant in your context as far as I can tell."You don't explain exactly what your understanding is, but you seem to be missing the concept.

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