To make fresh, clean drinking water from seawater, Sydney Desalination Plant uses reverse osmosis technology. Water from the Plant is monitored and treated throughout the entire process to meet Australian Drinking Water Guidelines, which makes it among the best in the world.
There are six key steps in the desalination process:
1. Seawater intake
Seawater is drawn from the Tasman Sea via four caged intake pipes located on the seabed, about 300 metres offshore and 25 metres below the sea surface. At full capacity, the intake pipes deliver about 600 million litres of seawater every day to the Plant via a 2.5 kilometre, 3.4 metre diameter concrete tunnel. The flow rate of seawater entering the intake tunnel is quite slow - less than one metre per second - and substantially less than seawater currents in the area. This allows the local marine life to swim out of the tunnel and not get drawn into the Plant.
2. Screening and pre-treatment filtration
Drum screens are used to remove any large materials that may enter the Plant through the intake tunnel. Typically, this is man-made rubbish and pieces of shells or plant matter from the ocean. We fill one small residential sized rubbish bin each month, on average. The Plant’s pre-treatment filter system removes any solid material, such as algae and small dirt particles, from the seawater. The aim is to get the seawater as clean as possible prior to the reverse osmosis process. The seawater is filtered through layers of filter coal (anthracite) and sand to prepare it for the reverse osmosis process. Wastewater from the pre-treatment filtration process is concentrated and put through a high-rotating centrifuge to remove as much liquid as possible. At the end of that process, the remaining sludge (made up of about 25 per cent solids and 75 per cent water) is removed for disposal.
3. Reverse osmosis
The clean filtered seawater passes through 36,000 reverse osmosis membranes so any salt and other minerals can be removed. The water is pushed at high pressure (60bar) through the semi-permeable membranes, which act as a filter for the salt and minerals and only allow fresh water to pass through. The intense pressure used during this process is enough project water 600 metres in the air. The water that is left behind from the process is effectively saltier seawater that is returned to the ocean.
The fresh water produced by the reverse osmosis process requires minerals to be added before it is fluoridated and chlorinated, in line with Australian Drinking Water Guidelines and NSW Health requirements. Water quality tests are carried out before the fresh water is sent to the Drinking Water Storage Tank, which can hold 40 million litres – the equivalent of 16 Olympic-size pools!
5. Water supply
Two large pumps transfer the water from the Drinking Water Storage Tank into an 18-kilometre pipeline that passes under Botany Bay and connects to the Sydney Water supply network at Erskineville. The water is then distributed to homes and businesses across Greater Sydney by Sydney Water.
6. Seawater concentrate
About 58 per cent of the water used during the desalination process is returned to the ocean. This water is known as seawater concentrate (effectively saltier seawater) and is transported back to the ocean via an outlet tunnel and specially designed outlet dispersion nozzles. These nozzles make sure the water mixes rapidly and returns to normal seawater salinity and temperature within a short distance of its discharge point so as not have an adverse effect on the local marine environment.
Our role in Sydney’s water supply
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Frequently Asked Questions
- Is the Sydney Desalination Plant operating?While the Plant was originally designed to operate only in times of drought, it has remained operational since 2019 to help address several storage dam water quality issues arising from bushfires, flooding and significant maintenance tasks in Sydney Water’s supply network.
The Sydney Desalination Plant’s WICA Network Operator’s Licence enables the Plant to remain operational, recognising that the Plant has always been, and will continue to be, an essential component of Sydney’s water management and an integral part of our city’s water-resilient future.
- How much water does the Plant produce?The Plant can provide up to 15 per cent of Sydney’s average drinking water needs without any reliance on rainfall.
It treats, filters and re-mineralises seawater to produce up to 91.25 gigalitres per annum of high-quality drinking water.
Under our WICA Network Operator’s Licence, the Plant will operate on a “flexible full-time basis”, producing between about 20 gigalitres to 91.25 gigalitres every year.
- What does desalinated water taste like?Sydney Desalination Plant water is treated to taste the same as Sydney’s other drinking water.
Like dam water, water from the desalination plant is treated to meet Australian Drinking Water Guidelines, which makes it among the best in the world.
- Who owns the Plant?Sydney Desalination Plant is jointly owned by the Ontario Teachers’ Pension Plan Board and the Utilities Trust of Australia, which is managed by Morrison & Co. Find out more on our About Us page.
- Why is desalination important?The Sydney Desalination Plant is Sydney’s only major sources of non-rainfall dependent drinking water. It is one effective way of securing Sydney’s water supply against the effects of climate change and natural disasters and the increase in demand due to population growth, warmer weather and urban greening projects.
While the Plant was originally designed to respond to Australia’s severe millennium drought, recent experiences have demonstrated that drought is only one type of event that requires support from the Plant to ensure clean and safe drinking water for Greater Sydney.
The Plant has been a reliable drinking water supply during floods and bushfires, which caused water quality challenges from time to time in Sydney’s storage dams.
- Where does the water go?The Plant can supply water to homes and businesses south of Sydney Harbour and as far west as Bankstown, as part of all their water supply.
Sydney Water uses a variety of water sources to supply customer needs. Where your water comes from depends on demand and where in Sydney you live.
If you live in the blue-shaded area on this map, you may receive water from the dams, the Sydney Desalination Plant or a combination of both. The Plant's water proportion will change throughout the day due to variations in supply and demand.
Everyone will benefit from desalination because it allows more water to be left in the dams, which means a more secure water supply for Sydney.
- How much energy does the Plant use?The Sydney Desalination Plant requires roughly 38 megawatts at full production and is 100 per cent powered by renewable energy.
The average energy needed to provide drinking water to one household is about the same as the energy used to run a household fridge.
- What’s the impact on the environment?Sydney Desalination Plant places a high priority on minimising any environmental impacts – both on land and in the water.
To support this, the Plant has put in place a world first stringent six-year marine environment monitoring program. The marine environment was monitored for three years before construction and three years after the Plant became operational. It demonstrated that the Plant has minimal effect on the marine environment.
On land, a third of the Plant site at Kurnell has been maintained as a conservation area. This area is protected, and native species of flora and fauna are regularly monitored. This includes a program to survey the numbers of grey-headed flying foxes and green and golden bell frogs in the area.