Water quality & filtration

We live in a world class city so it’s no surprise that our drinking water is some of the best in the world.

We protect our community by providing locally sourced, clean and safe drinking water to almost five million people every day.

  Lake surrounded by bushland

WaterNSW monitors and selects the highest quality water to send to us to filter. (Photo credit Adam Hollingworth, WaterNSW)

Most of the drinking water in Sydney, the Blue Mountains and the Illawarra comes from rainwater collected from natural catchment areas.

It’s then stored in local lakes and rivers that are surrounded by some of the most unspoilt, native bushland in the region.

Warragamba Dam provides 80% of Sydney’s drinking water.

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

WaterNSW protects the lakes and dams and uses its expertise to select the best quality source water for us to filter.

Water filtration plant

Our modern water filtration plants produce high quality drinking water.

It’s our job to make sure you have access to high quality drinking water that tastes great and is safe to drink straight from the tap.

We filter every drop to meet the Australian Drinking Water Guidelines, which are some of the strictest in the world.

We use modern water filtration plants and tailor the processes to the source water. This ensures we achieve a consistent, high standard.

Producing drinking water

Our water filtration processes can be different at each of our plants. We tailor the process to suit the quality of incoming water.

The quality of the incoming water could be different because of:

  • the types of activities in the catchment
  • natural minerals in the catchment
  • weather conditions, like droughts or high rainfall
  • natural hazards, like bushfires.

Filtration steps

We take many steps to produce great quality drinking water. We work around the clock and filter every drop.

  1. We use fine mesh screens to remove debris, like twigs and leaves.
  2. We adjust the pH to aid the filtration process.
  3. We add a solution (coagulant) that makes the smallest particles ‘stick’ together to form larger ‘flocs’. This makes it easier to filter them out.
  4. We use filters made of tightly packed beds of sand and crushed coal to trap and remove the floc. We clean our filters several times a week and continuously monitor their performance to ensure your water quality always remains high.
  5. We carefully balance the pH of the water.
  6. We add small amounts of chlorine to protect the water from harmful pathogens.
As a final step, we add small amounts of fluoride to the water as a safe and effective way of preventing dental decay. It’s not part of the filtration process, but is done under the advice of NSW Health.

Did you know?
Both chlorine and fluoride are natural substances that can be found in water and things you eat and drink every day such as teas and seafood. 

Find out about the water analysis in your area.

Make your own water filter

Using everyday items discover what makes a good water filter and learn how Sydney's water is filtered so it is safe to drink.

Request an excursion

Come behind the scenes at Orchard Hills Water Filtration Plant. Learn about our excursion requests.

Aerial view of Sydney desalination plant

Sydney Desalination Plant at Kurnell can provide up to 15% of greater Sydney's drinking water needs when dam levels fall 60%.

Sydney Desalination Plant was built to secure our water supply against the effects of climate change, a growing population and drought. It was built in response to the worst drought in 100 years, which saw Sydney’s dam levels fall to 34%.

The project was funded by the NSW Government and built by Sydney Water. It’s now owned by a consortium operating under the name of Sydney Desalination Plant Pty Ltd.

Unlike rivers and dams, the amount of water in oceans isn't affected by changing rainfall.

Desalination can give us a reliable supply of drinking water. In times of drought, Sydney's water supply can be topped up with water from the desalination plant when dam levels fall below 60%, as outlined in the Metropolitan Water Plan. Learn more about Sydney Desalination Plant.

The desalination plant uses reverse osmosis membranes to extract freshwater from saltwater. These membranes block dissolved solids like salt, so only freshwater can pass through.

The desalination plant uses advanced technology to ensure every drop meets the Australian Drinking Water Guidelines. Desalinated water matches our existing water quality, which is among the best in the world.

NSW Health also monitors water from the desalination plant to ensure it's safe to drink.

People testing water testing in laboratory

We continuously test our water in certified laboratories and report our results to NSW Health.

We continuously monitor your water quality. Our state of the art laboratory works throughout the year, doing up to 70 different tests to make sure your drinking water meets the Australian Drinking Water Guidelines.

We take samples from:

  • drinking water sources, including rivers and streams
  • water supply dams and storages
  • water filtration plants
  • the drinking water network
  • customers’ taps.

Our Sydney Water Monitoring Services™ laboratory is one of the leading water testing facilities in Australia. It provides a range of biological and chemical tests. Our laboratory and field sampling teams are accredited by Australia’s National Association of Testing Authorities.

We test for a range of water quality characteristics, guided by the Australian Drinking Water Guidelines. The guidelines:

  • set the standards for good quality drinking water
  • outline good practices for operating a water supply system
  • help protect public health
  • tell us how drinking water should look and taste.

The characteristics are categorised as physical, chemical and microbial.

Physical Chemical Microbial
Total dissolved solids
Dissolved oxygen
Free chlorine
Inorganic chemicals (dissolved salts)
Organic compounds

Find out more about the water analysis in your area.