What does an aquifer contain?

An aquifer is a geological formation that can store and transmit water, specifically groundwater. The primary characteristic of aquifers is that they contain fresh water found underground, which can be used for various purposes, including drinking water supply, agricultural irrigation, and industrial processes. Aquifers are typically formed in permeable rock or sediment, allowing water to flow through them and accumulate.

Freshwater is vital for sustaining ecosystems and human activities, making the presence of potable water in aquifers crucial. While saltwater, surface water, and polluted water might be encountered in different contexts, these options do not accurately describe the nature of aquifers, which specifically are known for their fresh groundwater reserves. Thus, the correct answer reflects the primary role that aquifers play in providing accessible fresh water beneath the earth's surface.