Water sources

Our main water sources

All water comes from the environment and flows through the natural water cycle. People manage this to make sure we have a safe and reliable water supply. Managing water in this way creates the urban water cycle. The urban water cycle takes water from many sources.


A catchment is an area of land, usually surrounded by mountains or hills, where all rainfall that runs off the land flows to a common point.

When rain falls in a catchment, it flows by gravity downhill – either over the surface or under the ground towards the ocean.

If the water flows on top of the ground, it's called surface water. If it soaks into the ground by infiltration, it collects in aquifers and becomes groundwater. Surface water and groundwater flow into waterways like creeks and rivers, or can be stored in water bodies like lakes, lagoons and wetlands. This freshwater eventually flows into the ocean where most of the Earth's water is found.

Most of Sydney’s drinking water comes from the Blue Mountains and the Southern Highlands.

The Hawkesbury-Nepean River system is the source of the largest volume of Sydney’s drinking water. This river system includes the Hawkesbury-Nepean River and all the smaller rivers that flow into it. They make up an area called the Hawkesbury-Nepean catchment. This large valley of over 22,000 square kilometres is larger than the whole of Greater Sydney.

The land use within a catchment affects the quality and amount of water in a river. It's important that all land use is managed carefully to make sure rivers remain healthy. Managing the impacts of all the activities around a river and its catchment is called total catchment management.

WaterNSW protects the health of our drinking water catchments. This ensures a reliable source of quality, fresh water is available for us to filter and supply to the people of Sydney, the Illawarra and the Blue Mountains. Find out more about managing catchments.

Play the Catchment Detox game and take on the challenge to manage a river catchment and create a sustainable and thriving economy.


Rain falling in river catchments is currently the main source of Sydney’s drinking water.

Dams are built across rivers to catch and store water to give us a more permanent and reliable water supply. Dams store water in an area behind the dam wall. This is often called a storage reservoir.

WaterNSW manages and protects drinking water catchments in NSW. Five of these catchments provide the source water for 11 major dams that supply water for Sydney, the Illawarra and the Blue Mountains. 

Sydney's dam water is filtered at one of our 9 water filtration plants to make sure it’s of excellent quality, clean and safe to drink.

Warragamba Dam is Sydney’s largest dam. It provides about 80% of Greater Sydney's water supply. The dam collects water from the Wollondilly and Coxs river systems and forms Lake Burragorang behind the dam wall.

Warragamba Dam is 65 kilometres west of Sydney in a narrow gorge on the Warragamba River. It's the largest urban water supply in Australia and one of the largest domestic water supply dams in the world. It holds 4 times more water than Sydney Harbour when it's full.

Some water also comes from smaller dams to the south of Sydney or in the Blue Mountains. These include CataractCordeauxAvon and Nepean dams.

Learn more about water supply catchments and dams at WaterNSW.

Avon Dam is one of 11 major dams in Greater Sydney.

Dam levels

Warragamba Dam’s water level rises and falls depending on the amount of:

  • rainfall in its catchment
  • water used by people in Sydney.

Since Warragamba was built in 1960, its lowest dam level was 32.4% on 10 February 2007. This occurred during a drought known as the Millennium Drought, which lasted from 1996 to mid-2010. In 2019–20, we experienced the effects of the worst drought on record.

Visit WaterNSW to check dam levels or check on rainfall and dam levels in the Greater Sydney CatchmentLearn more about water use and conservation.

Warragamba Dam was close to full in March 2012 and spilled for the first time since 1998.

Warragamba Dam dropped to about 42% capacity during the drought (mid January 2020).


The ocean can be used as a source of drinking water. Unlike rivers and dams, the amount of seawater in oceans is not affected by changing rainfall.

Desalination is the process of removing the salt from seawater to produce drinking water. It is a way to make sure people have enough water when:

  • countries do not have rivers that are easy to get to
  • countries are affected by drought
  • rainfall isn't adequate
  • populations grow faster than existing water supplies.

In response to the Millennium Drought, the NSW Government commissioned the Sydney Desalination Plant on the coast at Kurnell, between Botany Bay and the Tasman Sea. It can produce 250 million litres a day, which is about 15% of Greater Sydney's drinking water needs. While the plant is operating, we can adjust the capacity based on our system's needs.

Desalination has provided an extra source of water for Sydney that doesn't rely on rain. It's an important part of the NSW Government's plan to make sure we have enough water for the future.

Water from the desalination plant must meet the Australian Drinking Water Guidelines and Sydney Water’s standards.

97% of all the water on Earth is in seas and oceans.

Recycled water

Recycled water is water that's been used before. Recycled water is also another reliable source of water. We take wastewater or stormwater and clean it to a high standard so it can be returned to homes and businesses and safely used again.

There are many cities around the world that use recycled water as part of their drinking water supply. Some places you might like to learn more about are PerthSan Diego and Singapore.

We currently use recycled water in Greater Sydney for things like:

  • watering sports fields, lawns and gardens, including fruit and vegetable plants
  • flushing toilets
  • washing cars
  • filling ornamental ponds
  • fighting fires
  • washing laundry in a washing machine (you need the right plumbing for this)
  • making liveable cities with water features that make urban places cooler in summer
  • manufacturing.

We expect to use more recycled water in the future. Learn more about water recycling in Greater Sydney.

Recycled water is high quality.

Other sources

In Australia and in many other countries, water is scarce. People have developed many ways to collect and store water. These include groundwater and rainwater tanks.


Groundwater is water located beneath the Earth's surface. Some rain falling in catchments infiltrates into the ground and is called groundwater.

Groundwater collects in aquifers that are the spaces in rocks and between grains of sand and gravel. Groundwater slowly moves through these aquifers and flows into rivers, streams, lakes and wetlands. The top of the groundwater is called the water table.

Aquifers can store large quantities of water and can be the main source of water, particularly in dry areas. This groundwater can be used by people who build wells or bores to reach the water under the ground.

If groundwater is used in a sustainable way, it can be an important part of a city's water supply system.

Learn more about groundwater use from NSW Health.

Rainwater tanks

Rainwater tanks collect water that you can use in your garden.

Rainwater tanks can be a water source for drinking, flushing toilets, washing clothes or watering gardens. However, in urban areas it's usually unsafe to drink tank water.

This is due to higher levels of pollution in the atmosphere, which could pollute the tank water. NSW Health recommends that people use their public water supply for drinking and cooking because it's filtered, disinfected and generally fluoridated.

After long periods of drought, many people in Greater Sydney installed rainwater tanks. This water is used to water gardens, flush toilets, and helps conserve our drinking water resources. 

Learn more about rainwater tanks from NSW Health.

Rainwater tanks collect water that you can use in your garden.


An aquifer is an underground layer of water-storing rock or loose materials like gravel, sand or silt.

Teacher resources

Drinking water taste test (201KB) – set up a blind taste test as an experiment

Water on Earth video – did you know that all the water on Earth is all that we have?

Glossary – definitions of keywords and industry terms