Process Overview

Learn how we make fresh drinking water from seawater

The Sydney Desalination Plant uses reverse osmosis membrane technology to turn seawater into fresh water. There are several steps to this process.

  1. Seawater is drawn in from the Tasman Sea via an underground and undersea tunnel. Seawater enters the plant through screens that filter out larger material.
  2. Pre-treatment filters remove smaller particles.
  3. Filtered seawater is pumped into the reverse osmosis building.
  4. Waste from the pre-treatment filtration process are dried using a centrifuge and either reused or removed for disposal.
  5. Seawater is pushed at high pressure through reverse osmosis membranes to remove salt and minerals.
  6. Fluoride and minerals are added to the fresh water to meet Australian Drinking Water Guidelines and NSW Health's requirements. Remineralised water is then disinfected and transferred to the drinking water holding tank.
  7. Water is stored in the drinking water holding tank and then pumped to the Sydney Water network through a pipeline
  8. Seawater concentrate is returned to the ocean. 

Process Map

To learn more about each part of the process click on the steps below.

process diagram
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Step 1:

Seawater Intake

Seawater is delivered from the ocean through a 2 .5km long tunnel on the ocean floor. Water enters the intake at a flow lower than existing currents, so smaller marine life can easily swim in and around the intake without getting caught.

Seawater enters the plant through screens which filter out material larger than 3mm.

Step 2:

Pre-treatment

Gravity removes organics and fine particles by sand and coal filtration. A flocculant is added to the seawater to bind smaller particles together and make them easier to filter out.

Step 3:

Backwash / booster pump stations

The backwash pump station removes any built up particles.

Filtered seawater is pumped into the reverse osmosis building by the booster pump station’s centrifugal pumps. Here water pressure is increased to approximately 5 bar - the equivalent to diving to a depth of 50 metres.

Step 4:

Waste Treatment

Solids from the backwash water are thickened by gravity and then dewatered in a centrifuge before being removed for offsite disposal as solid waste.

Step 5:

Reverse osmosis building

Seawater is pushed at high pressure through many layers of synthetic membranes to remove salt and minerals. Fresh water passes through the membranes, while concentrated seawater (brine) is separated - this is called reverse osmosis.

The remaining concentrated seawater is directed to an energy recovery device before being returned to the ocean via the outlet tunnel.

Step 6:

Remineralisation

Flouride and minerals are added to the fresh water to meet Australian Drinking Water Guidelines and NSW Health’s requirements.

Remineralised water is then disinfected and transferred to the drinking water holding tank.

Step 7:

Drinking water tank and pump station

The water is stored in the 40 million litre drinking water tank and pumped into an 18 kilometre pipeline to transport the water to Erskineville and into Sydney’s drinking water network.

Step 8:

Outlet

Approximately 58% of intake water is returned to the ocean. It is twice the salinity and approximately 1 degree warmer. Water returns to normal seawater salinity and temperature within a 50 - 75 metre radius.

Take a virtual tour

Take a virtual tour of the  desalination plant see how it all works.

Related information

To find out more on the desalination process and infrastructure, take a look at: