A hydrogeologist explained to me that the earth could hold a lot more water with no appreciable rise in sea levels.
Basically, more water in the oceans means more water forced into the rocks under the pressure of gravity. He says that some 80% of the water on earth is locked up in the crust.
@Cripplecreek Actually, groundwater represents only about 0.75% of the earth's water....a tiny bit, compared to oceans. Oceans are about 97% of the water.
Now, if you are talking about deep water in the crust, or water bound up in mineral structures, etc., that's a different story, but those aren't part of the water cycle connected to the oceans.
Yes, we could sure use a lot of groundwater recharge, as we've used up a lot of our available fresh water, but that doesn't mean it can take up as much as you might think. The oceans are HUGE reservoirs, and thermal expansion alone would be considerable. And as meltwater from ice caps dumps into the oceans, we will get increased saltwater intrusion into coastal aquifers, ruining them for consumption (note that this would be small compared to the pumping we do in coastal regions, but it's addressing your hydro's point).
The way to offset
some of that rise would be if the rise in temperature leads to increased precipitation inland, recharging those aquifers that have been depleted.