As an egg is sitting in storage there’s a lot that’s happening to it.
An egg shell is porous, meaning that there is transfer of air and moisture between the outside and inside of an egg, and of bacteria (if present).
So as an egg sits or is stored, and that air transfer occurs, the main thing that will happen is that the egg’s air cell with grow larger.
The transfer of moisture out of the egg will expand the air cell and the space between the membranes in the egg.
Water is also transferred between the layers of the egg’s albumen.
To see this in action, crack a fresh egg on a plate. You’ll notice the yolk often sits very high on the albumen, which is the thicker white of an egg.
As the egg ages that albumen breaks down and you’ll often see a thinner, more watery layer of albumen.
Don’t worry, it’s perfectly safe if it’s more watery, it just usually is associated with an older egg.