Well, I'd never have guessed it but it seems it is porous to some degree:

from:
Q. Isn't granite porous? What about sealers?

A. Granite is the next hardest material to a diamond. There are some
granites that are more porous than others however, all of our granite
countertops are sealed during the fabrication process and again upon
installation. The rule of thumb is that when the water no longer beads up,
it's time to re-seal. For some folks that's two years, for some it's 4-5. It
depends upon usage.
http://www.instile.com/faq/faq04-porous.htm













But I'm sure it's not porous to the extent of "water seeping".