This chart is by month. Click on a different month to get the evap rate. http://www.cpc.ncep.noaa.gov/soilmst/efull_frame.html

As you can see, it varies from month to month. 25.4mm in an inch.

Here in June 2012 the evaporation rate was almost 3" for the month. (70mm)

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[Linked Image from lh6.ggpht.com]
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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).