Desalination solves a water problem by creating an energy problem.
The sea is an enormous water source, but its dissolved salts cannot be removed cheaply by ordinary filtration. Singapore therefore uses reverse osmosis, or RO: seawater is pressurised against membranes that allow water molecules through while rejecting most dissolved salts and many other contaminants.
PUB currently lists five desalination plants in Singapore and states that seawater RO uses about 3.5 kWh of energy per cubic metre of drinking water produced under the prevailing system benchmark.
The central engineering question is therefore not only “Can salt be removed?” It is “How much pressure energy can be avoided, recovered or reused while doing it?”
The public operating chain is: seawater intake → pretreatment → high-pressure pumping → reverse osmosis → fresh permeate → post-treatment → drinking-water network, while concentrated brine leaves the membrane stage carrying residual pressure and salt that must be managed responsibly.
1. Reverse osmosis fights natural osmotic pressure
If freshwater and saltwater are separated by a suitable membrane, water naturally tends to move toward the saltier side.
Reverse osmosis forces water in the opposite direction by applying enough pressure to the seawater side.
The pressure has to exceed the osmotic pressure created by the dissolved salts. That is why seawater desalination requires much more energy than filtering relatively fresh reservoir water.
2. Pretreatment protects the RO membranes
Seawater contains suspended particles, microorganisms and organic matter that can foul or damage membranes.
Desalination plants therefore screen and pretreat seawater before it reaches the high-pressure RO stage.
The exact treatment train varies by plant, but the principle is constant: expensive precision membranes perform better when larger and more easily removed contaminants are dealt with first.
3. High-pressure pumps are the energy centre of the process
The RO membrane does not suck freshwater out of seawater.
Powerful pumps raise the seawater pressure so part of the water passes through the membrane as low-salinity permeate.
The remainder leaves as a more concentrated brine stream.
Because pressurising such large volumes consumes substantial electricity, pump efficiency and energy recovery dominate desalination economics.
4. The membrane separates water from dissolved ions
A sand filter removes particles much larger than dissolved salt ions.
RO membranes operate at a much finer separation scale and reject dissolved salts and minerals while allowing water to pass through.
The result is very low-salinity water that can then be conditioned for drinking-water use.
5. The fresh side still needs post-treatment
RO permeate is not simply sent untreated into customers’ taps.
The water is conditioned so its chemistry is suitable for drinking and for distribution through the public water network.
The desalination plant therefore combines membrane separation with the same broader drinking-water objective as a conventional waterworks: produce water that remains safe and stable from plant to tap.
6. Brine leaves with more salt and still carries hydraulic energy
Not all incoming seawater becomes freshwater.
The rejected stream contains the salts removed from the permeate, making it more concentrated than the original seawater.
It also exits the RO stage under pressure. Throwing that pressure away completely would waste energy that the high-pressure pumps just spent electricity creating.
7. Energy recovery devices capture pressure before discharge
Modern seawater RO systems use energy-recovery concepts to transfer part of the brine’s remaining hydraulic energy back toward the incoming seawater stream or otherwise offset pumping demand.
PUB’s desalination research programme explicitly treats energy recovery as a major route for reducing the energy intensity of seawater desalination.
The important idea is circular: the process spends energy creating pressure, then captures as much useful pressure as practical before the concentrate leaves.
8. Energy recovery does not make desalination energy-free
There are unavoidable thermodynamic and equipment losses.
Pretreatment, pumping, controls and post-treatment also consume energy.
Energy recovery reduces the penalty; it does not eliminate the fundamental work required to separate freshwater from saline water.
9. Singapore currently has five desalination plants
PUB lists SingSpring, Tuas South, Tuas, Keppel Marina East and Jurong Island as Singapore’s five desalination plants.
The first plant, SingSpring, opened in 2005 and established desalinated water as Singapore’s fourth National Tap.
The plant portfolio provides a weather-resilient source that does not depend directly on rainfall or imported raw water.
10. Weather resilience is the strategic value
Reservoir yield falls during prolonged dry periods.
The sea does not disappear when rainfall drops.
Desalination therefore acts as a climate-independent supply source, trading higher energy demand for stronger resilience against drought and rainfall variability.
11. Keppel Marina East changes source according to weather
Keppel Marina East Desalination Plant is Singapore’s first large-scale dual-mode desalination plant.
During wetter periods it can treat freshwater from Marina Reservoir. During dry conditions it can switch to seawater desalination.
The plant therefore avoids paying the full seawater energy penalty when a lower-salinity source is readily available.
12. Direct coupling can eliminate unnecessary pumping stages
PUB states that Keppel Marina East directly couples its ultrafiltration and reverse-osmosis systems.
Removing intermediate break tanks and pumping stages reduces both space and energy use, making the process up to 15% more energy-efficient than a comparable arrangement with those intermediate stages.
Efficiency therefore comes not only from a better membrane but from removing unnecessary handoffs between processes.
13. Jurong Island uses co-location to reduce resource duplication
Jurong Island Desalination Plant is co-located with Tuas Power’s Tembusu Multi-Utilities Complex.
PUB states that the plant gains resource synergies including shared seawater intake and energy infrastructure, making it about 5% more energy-efficient than conventional desalination plants.
Industrial integration therefore becomes another energy strategy.
14. Solar power can offset part of plant electricity use
Jurong Island Desalination Plant also carries rooftop solar panels.
Solar does not remove the high-pressure requirement inside RO, but it can offset part of the electricity that would otherwise be drawn from the grid.
The distinction matters: energy efficiency reduces how much electricity the process needs; renewable generation changes where some of that electricity comes from.
15. PUB is still trying to push below today’s energy intensity
PUB continues funding research into desalination membranes, low-energy pretreatment, electrochemical methods and additional energy-recovery pathways.
In June 2026, PUB announced a new RIE2030 funding tranche for municipal and industrial water solutions, explicitly including desalination research.
The technology is therefore mature enough for national supply and still inefficient enough to justify major research.
16. Brine management is part of the environmental equation
The concentrate stream must eventually return to the marine environment under controlled conditions.
Because it is saltier than the intake water, discharge design and monitoring matter to reduce local environmental impact.
Desalination therefore shifts one constraint rather than making water from nothing: energy and brine management become the price of weather-resilient freshwater.
17. A worked example: one cubic metre of seawater feed
Imagine a volume of pretreated seawater entering the high-pressure RO system.
Pumps raise its pressure. Part passes through membranes as low-salinity permeate. The remainder leaves as concentrated brine still carrying pressure. Energy-recovery equipment captures part of that remaining hydraulic energy and uses it to reduce the net work needed on new feedwater. The permeate is post-treated before joining the drinking-water system.
The membrane removed the salt. The energy-recovery system reduced the cost of making the membrane work.
18. Common misconceptions
Misconception: Desalination is ordinary filtration with smaller holes.
No. reverse osmosis requires high pressure to overcome osmotic pressure and separate dissolved salts.
Misconception: All incoming seawater becomes drinking water.
No. part becomes permeate and part leaves as more concentrated brine.
Misconception: Energy recovery generates more energy than the process uses.
No. it recovers part of energy that would otherwise be lost and reduces net consumption.
Misconception: Singapore uses desalination because reservoirs failed.
No. desalination is one of four National Taps and adds weather resilience to a diversified water-supply portfolio.
19. The deeper idea: desalination converts water scarcity into an engineering budget
The sea makes water physically abundant around Singapore.
Salt makes that abundance unusable without work.
Reverse osmosis pays that work in pressure and electricity. Energy recovery, dual-mode source selection, process integration and co-location then try to return part of the cost.
Desalination is therefore not the discovery of unlimited free water. It is the decision that Singapore can engineer a dependable water source if it manages the energy bill carefully enough.