A ) Precipitation
The groundwater is predominantly replenished by the precipitation, so the amount of precipitation directly influences how much underground water there will be at a certain place.
The water from the precipitation falls on the surface of the Earth, but it doesn't stay there, instead, it is going through it down its layers, so if there's an underground tank formation from underground waters that is close to the surface, part of this water will get into it. The most common replenishing of the groundwater comes at the places that are dominated by limestone. The limestone is interacting with the water very easily, and the water manages to create cracks in it, so it goes straight through it and fills in the space inside it. These are actually the places where most of the springs appear.