How Water Changes Form: From Ice to Steam and Back Again

Water exists in three states: solid (ice), liquid (water), and gas (water vapour). Each state differs in shape and volume. Ice has a fixed shape and volume because its particles are closely packed. Liquid water has a definite volume but takes the shape of its container, as its particles are less tightly packed and can move around. Water vapour, the gaseous state, has neither a fixed shape nor a fixed volume; it spreads to fill any space available.
For example, ice cubes in a tray stay in their shape, water poured into a glass takes the glass’s shape, and steam from boiling water fills the kitchen. A common misconception is that water vapour is visible, but what we usually see is tiny droplets of liquid water suspended in air (like mist or steam), not the invisible gas itself.

Water changes its state through heating or cooling, and these changes are called melting, freezing, evaporation, condensation, and boiling. Melting is when ice (solid) turns to water (liquid) on heating. Freezing is the reverse—liquid water turns to ice on cooling. Evaporation is when liquid water changes to water vapour (gas) on heating, while condensation is when water vapour cools down to become liquid water. Boiling is rapid evaporation that happens at a specific temperature.
For example, when you leave ice out of the freezer, it melts into water. Water kept in a freezer turns into ice. Wet clothes dry in the sun because water evaporates. On a cold day, water droplets form on the outside of a glass filled with cold water due to condensation. Many students think boiling and evaporation are the same, but boiling happens at a fixed temperature, while evaporation can happen at any temperature.

The water cycle describes how water moves continuously on, above, and below the surface of the Earth. The main steps are evaporation, transpiration, condensation, precipitation, and collection. Evaporation is when the sun heats water in rivers, lakes, or oceans, turning it into water vapour. Transpiration is when plants lose water as vapour from their leaves. Both these vapours rise and cool, leading to condensation, where clouds form from tiny water droplets. When these droplets combine and grow heavy, they fall as precipitation—rain, hail, or snow. The water then collects in rivers, lakes, and oceans, starting the cycle again.
For example, after a rainy day, puddles dry up due to evaporation, and clouds form in the sky from condensation. Drawing a labelled diagram of the water cycle helps to remember these steps. Students sometimes forget that transpiration by plants is a key part of the cycle, not just evaporation from water bodies.

Dew, fog, clouds, rain, hail, and snow are all results of the condensation and freezing of water vapour in the air. Dew forms when water vapour in the air condenses into liquid droplets on cool surfaces, like grass in the early morning. Fog is made of tiny water droplets suspended in air near the ground, forming when air cools and water vapour condenses. Clouds form higher up when water vapour rises, cools, and condenses on dust particles. Rain happens when cloud droplets join together and become heavy enough to fall. Hail and snow form when the temperature is low enough for water droplets to freeze in the clouds before reaching the ground.
In real life, you see water droplets on a cold bottle taken out of the fridge because water vapour from the air condenses on its cool surface. Some students think dew comes from the ground, but it actually forms from water vapour in the air.