Which of the following best describes an unconfined aquifer?

An unconfined aquifer is characterized by its ability to receive direct recharge from surface water. This means that water from precipitation, rivers, lakes, and other surface sources can infiltrate through the soil and permeable rock layers directly into the aquifer. This process is vital for maintaining the water levels within the aquifer, as it allows for natural replenishment.

In contrast, an unconfined aquifer is also defined by the lack of an impermeable layer above it, which differentiates it from confined aquifers that have a layer of impermeable rock or sediment above, restricting flow from the surface. Therefore, while surface recharge is a hallmark of unconfined aquifers, the presence of an impermeable layer above them or containing only saline water fundamentally changes their characteristics and classification. Thus, the ability to be recharged directly by surface water makes option C the most accurate description of an unconfined aquifer.