A drop can take many routes—and it may remain in one place for a very long time.
Water is recycled through a network of stores and transfers. Energy changes its state; gravity helps move it through the landscape.
Water can be stored in oceans, lakes, rivers, glaciers, soil, groundwater, living things and the atmosphere. A transfer moves water between stores. Naming both ends of a transfer helps you explain a route instead of memorizing a circular picture.
During a physical change of state, water molecules remain water molecules. Their arrangement and movement change. Evaporation can occur at a liquid’s surface below its boiling point. Water vapour is an invisible gas; a cloud is made of tiny liquid droplets, ice crystals or both.
Identify a store, a surface transfer and an underground transfer. Watch how interception differs from infiltration.
National Science Foundation News · Open on YouTube →The Sun supplies energy that helps evaporate water. Air movement carries water vapour. Cooling can lead to condensation and cloud formation. Gravity pulls precipitation toward Earth and helps move runoff and rivers downhill. Groundwater responds to differences in elevation and water pressure.
Infiltration is water entering the ground. It can move farther downward through connected spaces. Below the water table, the ground is saturated: its open pores and fractures are filled with water. An aquifer is a permeable geological material that can store and transmit useful quantities of groundwater.
A drop may pass quickly through a small stream but remain in deep groundwater or ice for a long time. Residence time describes how long water stays in a store. A water-cycle diagram shows connections; it does not automatically show how much water moves or how fast it travels.
| Process | Change | Energy transfer |
|---|---|---|
| Melting | Solid → liquid | Energy absorbed |
| Freezing | Liquid → solid | Energy released |
| Evaporation | Liquid → gas | Energy absorbed |
| Condensation | Gas → liquid | Energy released |
Relevant pages from the original review pack. Use the updated explanations and linked sources for estimates and terminology.
Open the States screen and choose Water. Compare Solid, Liquid and Gas, then use the heating and cooling control. Watch the molecular arrangement as well as the thermometer.
Start with water as a solid. Add energy, then remove it. Describe two differences between the liquid and the gas without saying the molecules become different substances.
The moving symbols represent molecules. The drawing does not show their real size or every interaction. Use the state-change table in your notes to explain the energy transfers.
NASA Goddard · Scientific animation
Find one store and two transfers. Identify where energy drives a change and where gravity moves water.
Some precipitation infiltrates the soil, reaches a saturated zone and later moves as groundwater toward a stream. It does not have to become immediate surface runoff.
How can a tree connect soil water to the atmosphere?
Trace uptake, transport and water loss.
Roots absorb soil water; xylem carries water through the plant; transpiration transfers water vapour from leaves to the atmosphere.
Could a drop reach the ocean without first becoming surface runoff?
Yes. Infiltrated water can become groundwater, move through connected pores and discharge into a river or directly toward the coast. It can also remain stored for a long time.
Read further: USGS · Water cycle →
