With growing water scarcity, knowing how to filter salt water is more important than ever. Desalination technologies—from reverse osmosis and electrodialysis to membrane distillation and capacitive deionization—remove salts and other contaminants to make seawater or brackish water safe for drinking, irrigation, or industrial use. This guide explains the main methods, their pros and cons, and how to choose the right solution for your needs
Salt From Water: Core Desalination Technologies
You will see the same idea across all methods: separate the water from the salt. Some methods push water through a membrane. Others evaporate and re‑condense water vapor. A few use electric fields or charged surfaces to move ions.
Reverse osmosis (RO)
RO uses a semi‑permeable membrane that lets water pass but holds back salt ions. Reverse osmosis pumps supply pressure to “reverse” natural osmosis and force pure water to the low‑pressure side. A good seawater RO system can remove 99%+ of salts, including sodium and chloride, and many other contaminants (MDPI, 2024). Energy use for seawater RO is often in the range of 2.5–4.5 kWh per cubic meter when modern energy recovery devices are used. Brackish RO can be much lower.
RO works best with clean feed. You often need pretreatment: screens, cartridge filters, anti‑scalants, and sometimes ultrafiltration. After RO, water can be low in minerals, so many systems add a remineralization step to improve taste and protect pipes. RO does not always remove boron to safe limits in one pass because boric acid is weakly charged. Many plants use a second RO pass at higher pH or add a polishing step.
Large RO plants today produce huge volumes. In Saudi Arabia, government‑run facilities and partner plants report single sites making well over 600,000 m³/day. These mega‑plants serve major cities and industries.
Pros:
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High salt removal, proven at all scales
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Compact footprint for the output you get
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Works with many water types
Cons:
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Needs pressure, pretreatment, and careful brine handling
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Boron may need extra treatment
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Sensitive to fouling if feed varies
Electrodialysis and electrodialysis reversal (ED/EDR)
ED moves ions through ion‑exchange membranes using direct current. Cations move toward the cathode; anions move toward the anode. Fresh and concentrate streams form in alternating channels. The magic is that energy use scales with the number of ions you remove, not with the volume of water. So at low to medium salinity, ED can beat RO in energy.
EDR flips polarity on a schedule. That helps clean the membranes and reduce fouling. ED/EDR shines when the feed is brackish and you want stable output with fewer chemical cleans. You still need filters and anti‑scalants. You can also tune the process to leave a small amount of salt in the product if that is fine for your use.
Pros:
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Very efficient for low to medium salinity
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Handles variable feed better than RO in some cases
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Can target ions
Cons:
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Less efficient for very salty water
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Needs power supplies and controls
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Brine stream still needs a plan
Capacitive deionization (CDI)
CDI stores ions on charged electrodes, often made of porous carbon. Water flows between the plates; sodium and chloride ions stick to the surfaces when voltage is applied. When you reverse voltage or pause, the salt releases and you flush it out. New 3D‑printed, modular designs increase surface area and make systems easy to scale in the field.
CDI can be energy‑light for feeds below about 2,000 mg/L TDS (PMC, 2025). It can also be tuned to target certain ions, and new materials like carbon cloth electrodes are being studied to help remove boron, a contaminant that can harm crops at low levels. For many farms using brackish wells, CDI gives low operating cost and simple maintenance.
Pros:
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Very low energy for low TDS
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Modular; easy to expand
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Selectivity potential for certain ions
Cons:
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Not meant for seawater
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Electrode lifespan varies by feed
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Needs steady pretreatment to avoid fouling
Membrane distillation and forward osmosis
Membrane distillation (MD) heats the feed slightly and keeps the product side cool. A hydrophobic membrane lets vapor through but not liquid water, so salts remain. MD runs at low temperatures and pairs well with renewable heat: solar thermal, waste heat from engines, or warm industrial streams. It can reach very high salt removal, often 99%+. Reported lab and pilot modules show fluxes that translate to tens of liters per hour per square meter under the right conditions.
Forward osmosis (FO) uses a porous membrane and a strong draw solution to pull pure water through without high pressure. FO can handle tough feeds that foul RO. But you must later separate water from the draw solution. That add‑on step decides your energy and cost. FO is seeing use in special cases like disaster relief packs and some industrial loops.
Pros (MD/FO):
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Tolerant to high salinity and dirty feeds
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Can use low‑grade heat or novel draw solutions
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High salt removal
Cons:
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Often higher cost per cubic meter unless heat is free
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FO needs a smart draw recovery step
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Scaling risk on hot side (MD) without good control
Visuals & tools: Comparison table (salt removal %, energy, cost, use cases)
| Method | Typical salt removal (%) | Specific energy consumption (SEC) | Typical cost of water | Best use cases | Key notes |
| Reverse osmosis (RO) | 97–99.7 (single pass); >99.8 (two‑pass) | Seawater: ~2.5–4.5 kWh/m³; Brackish: ~0.5–2.5 kWh/m³ | Municipal: ~$0.5–1.5/m³ (site‑dependent) | Seawater and brackish, all scales | Needs pretreatment; add boron polish if required |
| ED/EDR | 95–99 (tunable) | ~0.5–2.0 kWh/m³ at low/medium TDS | Competitive with brackish RO | Brackish groundwater, variable feeds | Energy scales with ions removed; polarity reversal cleans |
| CDI | 85–98 (brackish) | ~0.2–1.0 kWh/m³ at low TDS | Low at small scale | Farms, small systems, low TDS | Modular; electrode care matters |
| Membrane distillation (MD) | 99+ | Thermal energy; electrical loads vary | Higher unless waste heat is free | Off‑grid, waste‑heat sites, very salty feeds | Heat‑integrated; strong removal across ions |
| Forward osmosis (FO) | 95–99 (depends on draw recovery) | Depends on draw recovery | Case‑specific | Portable kits, niche industry | Add a recovery step; good for fouling control |
SEC and cost ranges vary by design, geography, and power price.
When to use which: seawater vs brackish vs home systems
If your feed is seawater, use reverse osmosis or a thermal method like membrane distillation when you have heat. For brackish groundwater (for example 1,000–10,000 mg/L total dissolved solids), ED/EDR and CDI can beat RO on energy and cost. At home, under‑sink RO is simple and proven. In off‑grid cabins or at a camp, a simple distiller or solar still can make small amounts of distilled water.
Is reverse osmosis the best way to remove salt from water?
For most people, yes. RO is the most common way to remove salt from water. It gives high salt removal, stable quality, and works at many sizes. But “best” depends on your case. For low‑salinity water, ED or CDI may use less energy. If you have cheap heat, membrane distillation can be smart. If your key problem is boron, you may add a polishing step after RO.
Can you boil seawater to make it drinkable? (Why distillation, not simple boiling)
Boiling alone does not remove the salt. If you only boil and drink what is in the pot, you are still drinking salty water. You must collect the steam on a cool lid or tube and let it drip into a clean cup. That is called distillation. The salt stays in the pot. This process removes most salts and many metals. It also kills bacteria. The CDC explains this in their emergency water guidance.
Visuals & tools: 1‑page decision matrix and method picker
Use this quick matrix to pick a starting method. Adjust for budget, power, and brine rules in your area.
Method picker key:
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Feed salinity: “Low” < 2,000 mg/L; “Medium” 2,000–10,000 mg/L; “High” > 10,000 mg/L
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Scale: Home/Small < 5 m³/day; Community 5–500 m³/day; Plant > 500 m³/day
| Feed salinity | Scale | Best first pick | Second pick | Notes |
| Low | Home/Small | CDI | Under‑sink RO | CDI saves energy; RO is widely available |
| Low | Community | EDR | RO | EDR handles variable water well |
| Medium | Home/Small | RO | EDR | Pretreat for hardness and silt |
| Medium | Community | EDR or RO | CDI (modular) | Compare electricity cost vs membrane cost |
| High | Home/Small | Distillation | RO (countertop) | For very salty sources, distillation is simpler |
| High | Community/Plant | RO | MD with waste heat | Plan brine management from day one |
Home and Small‑Scale Solutions (DIY to Under‑Sink RO)
For home use, aim for simple, safe, and serviceable. In kitchens, the common fix is an under‑sink RO with a small tank. In off‑grid cabins, a countertop distiller or a solar still can help. If you camp near the sea, a pot, a lid, and a cup can turn saltwater into drinking water in a pinch.
Home reverse osmosis units: setup, maintenance, and costs
A typical unit has 3–5 stages: sediment filter, carbon block, RO membrane, and optional remineralization. Flow rates often range from 50 to 100 gallons per day for small systems. Waste ratios range from 3:1 to 1:1, depending on the design.
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Installation: mount under the sink, connect to the cold water line, add a drain saddle for reject water, and set the storage tank. Some systems use a small booster pump to improve recovery.
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Maintenance: change sediment and carbon filters every 6–12 months, the RO membrane every 2–3 years (or sooner if your feed is hard or dirty). Sanitize tubing and the tank yearly.
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Costs: purchase price varies; filter changes are the main ongoing cost. Expect low electricity use (mainly the pump).
Maintenance checklist:
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Replace prefilters on time
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Check pressure to the membrane
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Test TDS at the faucet
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Sanitize the tank and lines yearly
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Plan for cartridge recycling if available
DIY options: solar stills, simple distillation, and safety limits
A solar still is slow but simple. You pour salty water into a shallow tray lined with dark construction paper to help absorb heat. Cover with clear plastic so the water evaporates, condenses on the plastic, and drips to a clean channel. Under full sun, the output is small—think cups per day, not gallons. A countertop distiller is faster. It heats water to vapor and condenses it into purified water. Keep parts clean to avoid off tastes.
Simple stove‑top distillation:
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Place a small bowl in a large pot. Pour salty water around the bowl, not inside it.
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Place the lid upside down so the handle points down over the bowl.
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Heat gently. As water evaporates, it hits the cool lid and drips into the bowl.
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Use a low flame; do not let the pot run dry.
This process removes salt, metals, and kills bacteria. It is not fast, but it works in emergencies.
What is the cheapest way to remove salt from water at home?
If you need a few liters now and you have a stove, simple distillation in a pot is the cheapest. If you need steady daily drinking water, an under‑sink RO is the most cost‑effective over time. For zero power, a solar still is nearly free after you build it, but it is very slow.
Gardening use‑case: boron removal for sensitive crops
Many crops are sensitive to boron, even when humans consider the water safe. Aim for under about 0.5–1.0 mg/L for sensitive plants. If your well water shows high boron, one plan is RO followed by a small selective filter. Some CDI modules with tuned electrodes can also help remove boron. Always test both feed and product. Start a trial on a small plot before switching a full orchard.
Advanced Materials and Case Studies (Boron, Novel Membranes)
Some ions are stubborn. Boron is a known case. It exists in seawater at levels often above drinking and crop targets. Standard RO can struggle because boric acid is not fully charged at neutral pH.
Case study: Carbon cloth electrodes selectively removing boron
New carbon cloth electrodes in lab studies can target boron. The idea is to add a polishing step after RO. This meets WHO drinking water advice and helps farmers grow sensitive crops. It can also lower chemical use because you avoid large pH shifts in a second RO pass. In field pilots, such selective removal steps helped irrigate berries and almonds within safe boron ranges with less waste.
Emerging membranes: biporous and low‑energy RO
Researchers are testing biporous membranes that let vapor pass with low heat. Others are designing RO membranes with higher permeability, so you get the same flow at lower pressure. Some labs report high removal (up to 99%) at room temperature with new materials. Scale‑up is in progress, with pilot lines focusing on stable flux, foulant resistance, and cost per square meter.
Performance benchmarks: newest RO mega‑plants in Saudi Arabia and Israel
Large plants in the Middle East show high recovery at low energy per cubic meter thanks to energy recovery devices and tight pretreatment. Saudi systems operated by public agencies and partners report site outputs above 600,000 m³/day. Plants in Israel operate at large scale as well, with careful intake design and brine mixing to protect coasts. These benchmarks give confidence to cities planning their first big plant.
Energy, Cost, and Sustainability of Desalination
Energy and brine define the footprint of any system. A smart plan starts with the salt load of your feed, your recovery target, and your local energy mix. Then you tune pretreatment, membranes or electrodes, and brine handling to hit your cost per cubic meter and your emissions goal.
Energy footprints: RO vs ED/EDR vs CDI vs membrane distillation
Energy per cubic meter goes up with feed salinity and recovery. For seawater RO, expect about 2.5–4.5 kWh/m³ with modern energy recovery. For brackish RO, it may drop to 0.5–2.5 kWh/m³. ED/EDR often uses 0.5–2.0 kWh/m³ at low to medium salinity, since it removes ions rather than pressurizing a membrane. CDI can be as low as 0.2–1.0 kWh/m³ at low TDS, but it is not meant for seawater. Membrane distillation uses thermal energy; the electric draw depends on pumps and fans. If you have waste heat, the added electric demand can be small.
Recovery rate also matters. Higher recovery means less brine volume, but salt concentration rises. That can raise scaling risk and cleaning needs. There is a sweet spot where total energy and downtime are both low. You find it by testing a few recovery points during commissioning.
Cost drivers and optimization levers
Capital costs: membranes or electrodes, pressure vessels, pumps, reverse osmosis skids, anode and cathode power supplies (for ED/CDI), and controls. Operating costs: electricity or heat, filters, anti‑scalants, membrane cleanings, and labor. Membrane lifespan and fouling rates drive both cost and downtime. A small investment in pretreatment often lowers long‑term cost.
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Pretreatment: a simple, well‑run filter line keeps fouling down, lowers chemical cleans, and protects membranes.
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pH and anti‑scalants: the right pH and dose can raise recovery without scaling.
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Stage design: two‑pass RO helps hit tighter targets like boron or nitrate.
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Brine concentration: partnerships with salt producers or zero‑liquid‑discharge (ZLD) vendors can cut discharge fees.
Brine management and environmental impact
Brine is concentrated saltwater with any added chemicals. Discharging to the ocean needs careful mixing and monitoring to protect seafloor life. For inland plants, options include deep‑well injection, evaporation ponds, or ZLD systems that crystallize salts. Some sites recover salt crystals or other minerals (for example, gypsum). Others combine brine with carbon capture streams for joint treatment, though this is still developing. Good design uses outfalls that spread brine and mix it fast to avoid dense layers on the surface or bottom.
Standards, Testing, and Health Considerations
A safe system meets health limits and tracks performance. Water quality is more than removing salt; it includes trace ions, metals, and microbes.
Drinking water quality: WHO/Ministry of Health limits (TDS, boron, sodium)
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WHO offers guidance values for taste and health. For TDS, there is no health limit, but water tastes best below about 600 mg/L.
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For boron, WHO advises a health‑based value around 2.4 mg/L for drinking water. Many countries and farms set lower targets for irrigation.
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For sodium, drinking water has no strict health limit for the general public, but people on sodium‑restricted diets may need lower levels. In daily life, most sodium comes from food, not water.
For farms, FAO guidance offers crop‑specific targets for boron and salinity. Sensitive crops may need boron below 0.5–1.0 mg/L and low electrical conductivity.
Monitoring and QA/QC: sensors, sampling, and certification
Simple tools go far. A handheld TDS or conductivity meter gives quick checks. Online sensors on pressure and flow help catch fouling early. For boron, lab assays or specific test kits give better accuracy. Membrane integrity tests catch pinholes. Keep a log of filter changes, cleanings, and test results.
Is desalinated water safe to drink long‑term?
Yes, when it meets national standards and is properly managed. Desalinated water is often remineralized for taste and to protect your body’s mineral balance and plumbing. Cities serving millions rely on it every day. The key is good pretreatment, stable operation, and regular testing.
Extracting Salt (Not Water): Solar, Vacuum, and Mining Methods
Some people want to separate salt and water for the salt itself. In that case, you want the salts left behind, not the pure water. There are three main methods: solar ponds, vacuum pans, and mining or solution mining.
Solar evaporation ponds: climate needs, yield, and purity
In dry, windy places, large shallow ponds evaporate seawater. As water evaporates, minerals precipitate in steps. First come calcium compounds, then sulfate salts, then table salt (sodium chloride), and finally magnesium salts. You rake and move each layer. Yield depends on sunlight, wind, humidity, and pond design. You can shape ponds so separate layers form in zones. This method is simple but needs land and the right climate.
Vacuum evaporation: how vacuum lowers boiling point for refined salt
Industrial salt makers often use vacuum evaporation. They boil brine in vessels under vacuum. Lower pressure means a lower boiling point, so they save energy. Crystallizers control purity and grain size. You can produce food‑grade or industrial salt by adjusting seed crystals and temperature profiles. Waste heat from other processes can help offset energy use.
Rock salt and solution mining: drilling, leaching, and brine purification
Rock salt sits in underground beds. Solution mining pumps water to dissolve salt, then lifts brine to the plant. You soften and purify the brine, then crystallize salt with pans or vacuum units. Safety and environmental controls matter: plan for subsidence, protect aquifers, and manage heavy minerals. Some sites mine solid rock salt, crush it, and screen by size.
FAQs
1. How to remove salt from water?
To filter salt from water, the most common approach is reverse osmosis or distillation. In distillation, water is heated to evaporate, leaving salts behind. The water vapor is then collected by condensation. Another way to separate salt is using membranes that are selectively permeable, allowing water to pass while salts remain. This process does not necessarily remove all trace minerals, but it performs the purpose of reducing salt content for safe drinking. In research, methods like decanoic acid extraction are explored, but for everyday use, evaporating water and collecting the condensation is relatively simple.
2. Why is salt called the silent killer?
Salt can cause high blood pressure when consumed in excess, which often shows no clear symptoms, hence the term “silent killer.” Regular intake of water that contains high sodium may affect the body subtly over time. Even when people add salt for taste, the cumulative effect can be significant. Biomedical sciences studies highlight that monitoring salt intake is critical to prevent cardiovascular issues. The bond between sodium and chloride in water or food contributes to the health risk, making it essential to treat high-salt water or diet to protect long-term health.
3. How to get salt out of water naturally?
A natural method to remove salt from water is to let the water evaporate under sunlight. As water evaporates, the salt remains, and you can collect the water by condensation for drinking. Another way to separate salt uses simple solar stills, where evaporated water is directed onto a surface, collecting the condensation in a clean channel. This process does not necessarily require complex equipment but takes time. Boiling water and capturing steam is another option, though it consumes more energy. Relatively small amounts can produce safe water for home or field use.
4. How to turn water into salt?
You cannot chemically turn water into salt. To “turn water into salt,” you must remove water so that the dissolved salt crystallizes. By evaporating water naturally or by heating, you concentrate the salt. Collecting the condensation gives pure water, leaving tons of salt behind. This process does not involve adding salt to water to create it but relies on separating water from the salt solution. In experimental setups, decanoic acid or other agents are studied to perform selective ion removal, but for practical purposes, evaporation is simple and effective.
5. Does fresh water have salt?
Yes, fresh water contains small amounts of dissolved salts and minerals, typically below 500 mg/L TDS. These salts come from rocks and soils, forming natural ionic bonds with water molecules. Although the concentration is low, it can affect taste and slightly impact the body. Fresh water can be treated to remove even these small amounts, for example, using reverse osmosis or filtration. The process to remove salt is relatively simple and safe, involving water to evaporate or permeable membranes to perform selective separation, ensuring safe water for drinking or biomedical purposes.
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