How to re attach faucet base to granite counter top?

Faucets aren’t typically glued down to counter surfaces, because you’ll likely want to change facets before you’ll want to change counter tops. Usually, a roll of “plumber’s putty” is pressed between the faucet base and the counter top to form a seal that prevents water from leaking under, then nuts secure the faucet from underneath the counter top. The plumber’s putty is non-adhesive and removable.

You could easily get some putty at any hardware store (it’s cheap), and re-seat the faucet, making sure that the nuts are securely tightened. The nuts should be doing the lion’s share of the work of holding the faucet in place, with a little bit of help from the putty.

You could go with one of the epoxy putties that are on the market, but the faucet would be forever wed to the counter.

Before you go and use plumber’s putty, look underneath your sink look where the faucet comes through the counter top. You should have a lock nut/washer that threaded onto the faucet which secures it to the counter top. Make sure to tighten that first, and then apply a clear silicone adhesive seal around the top of base of the faucet on the counter top for a secure seal. BTW you might have to pick up a special wrench to tighten the nut, if you can’t do it by hand.
Good Luck!
R