Water cycle | Murray-Darling Basin Authority

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THE WATER CYCLE

WATER GOES 'ROUND & 'ROUND

Water moves around the Earth continuously. It moves in one of three different states –

liquid, gas or solid

This continuous movement is called the water cycle.

Water can move between the following states –

from a liquid to solid
from a liquid to gas
from a gas to liquid
from a gas to solid
from a solid to gas.

Changes in temperature cause the changes in states.

For example, liquid water in the ocean or a lake heats and evaporates to become a gas, rising into the atmosphere.

It then condenses to form clouds which return the water to a liquid state in the form of rain. It may also form a solid as hail or snow that falls back down to the ground where it melts, turning back to liquid.

THE MAIN PROCESSES OF THE WATER CYCLE

EVAPORATION

Evaporation happens when liquid water is heated. The heat turns the liquid into a gas that rises into the air as water vapour.

The sun provides the heat that evaporates the water from the ocean, lakes, rivers, swimming pools and plants, as well as the washing on your line, and from our bodies.

Plants also contain water which evaporates from their leaves. This is called transpiration.

CONDENSATION

Condensation of water happens during cold weather. When the temperature is lowered, water changes from a gas into a liquid.

Clouds are an example of condensation. High in the atmosphere the air is cooler and the water vapour in the air groups together, condensing into clouds. When large groups of molecules form, the water falls as precipitation – rain, hail or snow.

Other examples of condensation are the drops of water that form on the outside of a cold drink bottle or can, or the steam/fog on the mirror or wall in the bathroom after a shower.

PRECIPITATION

Precipitation (rain, hail, snow) occurs when large groups of water molecules condense (come together) and become too heavy to remain in the atmosphere. Clouds become heavy and gravity pulls the water down to Earth.

COLLECTION

When water falls back to Earth as precipitation, it may fall anywhere, such as in the ocean, rivers, lakes, or on land. When it falls on land, some water will soak into the ground and eventually become part of the groundwater system, some will fall in the ocean and some will run over the soil collecting in rivers, lakes and wetlands. This is surface water. The water cycle will then begin again when the water evaporates from these collection areas.