[Jack Hydrazine]

Check out this table on the weight and density of water at various temperatures.

http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

[Myrddin]

I found that one as well before my reply that the quoted weight was correct. My error was assuming the density is 1.0. That works fine when measuring in grams vs cubic centimeters. I was surprised to hear that 8 lbs of water isn’t volumetrically a gallon.