Tuesday, March 30, 2010

Water Use Report

Recently the USGS released a report on water use in the U.S.  The press picked the headline:  "U.S. Uses Less Water Today".  The report is actually using 2005 data and comparing it to data in previous 5-year blocks of time.

From one of the press releases:  "The report concludes...even though the amount of irrigated acres has increased, irrigation application rates have steadily decreased - a change that the report's authors attribute to the increased use of more efficient irrigation systems.


"We are pleased to see that irrigation efficiency played such a major role in decreasing our nation's overall water use" (John Farner, Irrigation Association).  

Inside the actual report we find recognition that irrigated acres have been increasing.  And inside the guidelines for the preparation of the 2005 report we find the statements:  "Irrigation withdrawals include conveyance losses." and "Data for the optional elements...will not be part of the national water-use analysis for 2005..." and in the mandatory elements we find "Ground-water total withdrawals.. [including conveyance losses]" and in the optional elements we find "consumptive use, by county" [not part of the report].

What seems to be really happening in this report is that the conveyance losses are being reported as use and the consumptive uses are being ignored.  Sure, irrigation efficiency will reduce conveyance losses, thus appearing to "use less water", but the real question is what's happening to the amount of actual consumptive water use?  This is the vital number that relates to long term supply and the health of any hydrologic system. 

My guess is that while pumped (diverted) water is actually less, the application of the less water on more acres is likely to result in increased consumptive water use.  Yes, you get more production from each unit of water as efficiency increases, which is a good thing, but you don't consume (use) less water.   

The judicious use of the phrases "water use" and "consumptive use" are in the report, and I think the distinctions are made - but far too subtely for most to recognize.  So the press simply concludes that water use is reduced. 

I think this is the wrong message to be sending and it leads to more money and effort put to irrigation efficiency (in the name of water conservation) in areas where reducing consumptive water use is most important.  This is one reason why water management continues to be so difficult.

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