## TL;DR

The water (hydrologic) cycle describes continuous movement of water on, above, and below Earth's surface. Processes: evaporation (liquid→vapor), transpiration (from plants), condensation (vapor→liquid, forms clouds), precipitation (rain, snow), infiltration (into soil), runoff (to rivers/oceans). Earth's total water volume: ~1.386 billion km³.

## Core Explanation

Oceans: 96.5% of all water. Freshwater: 2.5% — mostly locked in glaciers/ice caps (68.7%) and groundwater (30.1%). Surface freshwater (lakes, rivers): only 0.3% of freshwater. Average residence time: oceans ~3,200 years, atmosphere ~9 days. Groundwater: crucial for drinking/irrigation, threatened by over-extraction and pollution. Climate change intensifies water cycle — more floods and droughts.

## Further Reading

- [NASA Earth Observatory — Water Cycle](https://earthobservatory.nasa.gov/features/Water)