Why does water drawn from an aquifer differ in quality from surface freshwater

The quality of water drawn from an aquifer differs in quality from surface freshwater because the surface water contains a lot of contaminant. Even when a ground water contains contaminants in it, it is filtered by the rocks in underground.

Explanation:

The water that are in river, ocean or any other water from surface level is known to be a surface water. This water is subjected to the exposure of many contaminants as they are directly on the earth's surface. These are known as "soft water" and they usually contain more minerals. The surface water can be contaminated by waste of humans, animals, industry wastes, etc. Hence they have low quality.

A Deep well drilling must be done in order to take water form the Large aquifers that are present Groundwater. The ground water also contains contaminant. But, the quality of these water is high since the rocks and soil found underground filters and removes the contaminates that are present in an underground water.