What percentage of the human body is water?

An average adult body is 50 to 65 percent water -- that's roughly 45 quarts. Men are more watery than women. A man's body is 60 to 65 percent water, compared to 50 to 60 percent for a woman. In infants, the figure is a whopping 70 percent according to statistics compiled by the International Bottled Water Association.

http://water.usgs.gov/edu/propertyyou.html

The dreaded 'more information than you need'

Percentage of water making up tissues, organs, fluids and bone in the human body: Brain 75%, Heart 75%, Lungs 86%, Muscle 75%, Liver 85%, Kidney 83%, Bone 22%, Blood 83%, Saliva 95%, Perspiration 95%

https://en.wikipedia.org/wiki/Body_water