check and see if one of the faucets is leaking. the water has to be coming from somewhere.

once you fix the leak the stone should dry out on it's own in 3-5 days. (you can speed it up with a blow dryer.)

There is also a distinct possibility that the stone is not actually granite.

Actual granite does not absorb water.

This is one of the reasons that you need to test stone samples beofre settling on one.

The stone industry often labels many stone that requires diamond tooling to work as 'granite' when they are actually other stone types and do not have the desirable characteristics of actual granite.

What granite is it?

Wow, that looks like a lot of water. I agree that you need to determine where the water is coming from. Sealant does not necessarily seal out water. I have a sealed marble bathroom counter and sometimes water will slightly darken the stone. However, it's usually little bits here and there and it dries in quick order. You have a TON of darkness. I agree with oldryder that you should check if your faucet is leaking.

Is this water getting under the sealant? That's what it looks like.
It confuses me, because granite doesn't absorb water, yet something's holding it.

I think I'd be talking with the fabricators, too.
This is a new one (to me).

Also, what type of sealant are you using? Is it an impregnating sealer? How does the water behave on the other parts of the counter? Was the stone slab treated with a resin? It appears to be honed.