The Water Cycle


Water cannot be created or destroyed, it can only change state between solid (ice), liquid (water), and gas (steam).

The dictionary says that a cycle is "a series which returns upon itself". This is why we call the natural transfer of water around the planet the Water Cycle.

Did you know that scientists have calculated that there is the same amount of water today as when dinosaurs roamed the planet? This means that the water falling in your shower tonight could once have fallen as rain on a Tyrannosaurus Rex!

Below is a broad description of the Water Cycle. It explains the complex process of where water comes from, at what stage it's treated, how it reaches our homes, and how it's part of a never-ending cycle of precipitation and evaporation.


This is the process by which energy from the sun (solar energy) turns liquid water into water vapour. As the water molecules get hotter, they begin to move faster in the liquid. They collide more often with each other, and, gradually some water molecules move fast enough to break away from the others. They escape into the air - that is they have evaporated. More than 80 per cent of the water vapour in the atmosphere is from water evaporated from the oceans. When this water evaporates the substances dissolved in it (like salt) remain behind.


Water is absorbed through the roots of plants and moves up through hollow tubes to the leaves. The movement of water up the plant is due to capillary action.

Leaves have small holes in them through which they can absorb carbon dioxide and release oxygen. Water vapour is also lost through evaporation from the pores of leaves. The process of water movement and loss from plants is called transpiration.


When water vapour which has been evaporated from surface waters or transpired by plants undergoes a decrease in temperature in the atmosphere, water droplets form. Water condenses into these droplets only when there are small dust particles present, around which the droplet can form. These very small droplets of water are suspended in the atmoshere. When millions of droplets come together, they form the clouds we see in the sky, or fog we see at ground level.


If water droplets in clouds join together to form drops between 2 and 6.5 mm in diameter, they may fall as rain. Fog or mist is really just low lying clouds. Hail forms when droplets of water freeze around a small core of ice. Hail stones increase in size by adding extra layers of ice as they are tossed up and down by rising and falling air currents common in thunderstorms. Dew is formed when water vapour condenses near the ground. On clear nights, the land will rapidly lose heat to the air. Any moist air near the surface will cool and condensation will occur. Frost forms when the surface temperature falls below freezing (0°C) resulting in ice crystals directly forming from the saturated air.


A lot of the water falling as rain can run off the ground surface either into rivers, lakes or into the ocean. Nearly 40% of all precipitation flows back across the land to seas and oceans.


Some water falling as rain on the earth soaks into the ground through the soil and underlying rock layers. As the water infiltrates through the soil and rock layers, many of the contaminates in the water are filtered out, helping to clean the water. When so much water has infiltrated the ground that no more can soak in, then it is said that the ground has reached saturation point and any additional water will be forced to run over the surface as Run-off. Some of the water which infiltrates into the ground ultimately returns to the surface as springs or lakes and can also drain into river systems below the surface of the river flow. Some of the infiltration water will remain underground as Groundwater.


Water is pumped from the rivers and stored in dams for use in the water supply system.

Water treatment

Stored Water is made safe to drink at the Water Treatment Plant.

Reticulation of water

Through a series of pumps, gravity pipes and reservoirs, water is supplied to domestic, commercial and industrial users.

Sewage collection

After use in the household or commercial organisations, waste water is collected and transported for treatment via a complex system of gravity mains and sewerage pumping stations.

Sewage treatment

Sewage is treated at Water Recycling Plants located at various locations throughout the city.

Reuse of recycled water

Recycled water is used on a number of sporting fields, golf courses and other commercial enterprises in the community, reducing the amount of fresh drinking water these properties need to use.

Deep sea release

Recycled water that is not reused is then released to the ocean via a deep sea release pipeline.