How long do molecules of groundwater stay in the ground?

It varies from days to years

Explanation:

Water cycle includes series of steps and processes which enables water to be recycled. During dry or hot season , the sun heats up water bodies and water evaporates into the atmosphere.

During the cold or rainy season the evaporated water condensed and fall as rain back into the water bodies and environment generally.

The period or time frame in which ground water from rain stays in the soil is based on some factors such as the nature of the soil. Some soils such as clayey soil have a larger water retentive capacity than the others.