Granted, Christmas trees do appear to "drink" water fairly quickly.  But the
absolute volume is not really that much, considering the size of the tree -
since the reservoirs hold perhaps a quart of water, after displacement by the
tree trunk.

And just because they drink this water doesn't mean it actually >>>makes an
observable difference<<<.    The absolute weight differential, in percent
terms, is negligible (although much of the water may be aspired).

Has anyone ever bought two trees, watered one and not the other, and then
tested for brittleness around January 15th?

c