What are the advantages and disadvantages of using groundwater as a source of freshwater?
Advantage: amount, disadvantage: overuse
It's pretty difficult to visualize just how much water is stored underground, but one can try. The water in the Ogallala Aquifer, which covers much of the midwest and south, is greater than all of the water in the all of the Great Lakes combined.
Another advantage is it's easy to purify because the water in aquifers is usually very clean to begin with. It's not usually contaminated with viruses, mud, chemicals, etc..
There's a problem, however, and it's entirely our fault. We think there is so much water in these aquifers that we can pump it out endlessly, which is not at all true. The city of Los Angeles was growing massively in population in the 1900s to the point where they actually ran their water source completely dry. Their source? An aquifer. No matter how much water is in an aquifer, a large, high-consuming human population can deplete it, much like what's happening with coal and oil, both of which we had thought to be endless. Overuse is a big issue.
The other problem is contamination, which almost always comes from human sources. Aquifers have recharge zones that are often quite far from the aquifer itself due to the formations of the rock layers. If we build a factory or a landfill in one of these zones, the chemicals have a good chance of leaking, and will eventually make it to our groundwater. The problem is that once a chemical contaminates an aquifer, it's contaminated forever.
The bottom line: aquifers are great because of the amount of clean water we can get from them, but our own tendency to overexploit and contaminate our natural resources create disadvantages.