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5 Quick Questions – How do you turn seawater into drinking water?
Q: There’s a couple of different ways you can remove salt from seawater to make drinking water. What method does SDP use?
A: SDP uses a two-pass reverse osmosis (RO) process to remove salt from sea water prior to post-treatment to produce drinking water. To improve the quality of the treatment process the sea water is first filtered to make it as clean as possible – to remove insoluble material (suspended solids). The filtered water is then pushed through 36,000 semi-permeable reverse osmosis membranes to produce permeate. Most of this water is further processed through a “second pass”, which is another RO system used to further treat or “polish” the permeate produced from the first pass. This water is then treated to make it suitable for human consumption.
Q: How does reverse osmosis work?
A: Reverse osmosis is the process of purifying water through a semi-permeable membrane to remove unwanted contaminants. Due to the high concentration of dissolved materials in sea water, the system requires very high pressure (60 bar) to be applied to the feed side of the membrane to push the water through the membranes. The fresh water produced is called permeate while the leftover water, concentrated with dissolved materials, is referred to as seawater concentrate or brine.
Reverse Osmosis membrane vessels
Q: How long does the process take?
A: The process of drawing in the sea water, removing the suspended solids and dissolved solids and treating it to produce potable water depends on the flow that the plant is operating at any given time. At minimum flows, it takes about 12 hours from the time sea water is pulled in from the ocean to produce potable water, but at maximum plant capacity this time is reduced to less than 4 hours.
Q: How much energy is required during the reverse osmosis process?
A: The energy consumption of the plant is also linked to the flow the plant is operating at the time. The plant consumes anywhere from about 10MWh to 40MWh of energy, with a specific energy consumption of 3.4 MWh/ML of water produced. Given the energy intense nature of the treatment process, it is important to mention that SDP is powered by 100% renewable energy. This energy is provided by the Capital Wind Farm, which is one of the largest in NSW.
Q: What happens to the salty water that’s left over once the reverse osmosis process is complete?
A: The leftover salty water is known as seawater concentrate or brine. At SDP, approximately 58% of the water is returned to the ocean via an outlet tunnel structure, where it is dispersed through an array of nozzles under a mechanism that ensures the brine mixes adequately with the surrounding waters to ensure no negative impact to the immediate surrounding environment. A world-first six-year study was completed by University of NSW. This study thoroughly examined the plant’s desalination process and found that there were no significant impacts on the local marine environment.
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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. 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.
Acknowledgement of Country
We acknowledge the Gweagal clan of the Dharawal people as the traditional owners of the land on which the Sydney Desalination Plant sits and we pay our respects to elders past and present.