I'm hoping you mean the outline of a beach ball when you refer to size. A three-dimensional beach ball would be a couple of gallons/many liters! For A/C condensation, that's not unusually large in high humidity conditions.
It's a good sign that you are seeing the water. It should be clear, as it is, as Paulster suggested, condensation from the humidity of the atmosphere. The water drain is working on your evaporator inside the vehicle, rather than leaking into the passenger cabin.
Compare the amount of water you see on the ground with what you see on the outside of a cold drink. Those days when your drink is dripping condensation are the same ones you'll see increased volume under your vehicle.
You may also be able to note other vehicles (if running) in the area with puddles. On a humid enough day, the duration of a red traffic light is sufficient to create a puddle on the ground.
By confirming that your reservoirs are not leaking, you've narrowed it down correctly to the A/C.