Seawater desalination systems use special membranes, like tiny filters, to separate dissolved salts and other stuff from ocean water. This process needs high pressure, usually 800-1,000 psi for seawater, to push the water past the salt. Here’s how a standard seawater RO system works:
- Intake: Raw seawater comes in from the ocean, either through an open intake or a beach well.
- Pretreatment: Filters like multimedia and cartridge filters, plus chemical doses, remove dirt, organic matter, and tiny living things.
- High-Pressure Pumping: A strong pump pushes the pretreated water to 800-1,000 psi.
- Reverse Osmosis: Water goes through SWRO membranes. These membranes block 99.5-99.8% of the dissolved salts.
- Energy Recovery: The salty water that gets rejected still has a lot of energy. Energy recovery devices (ERDs) capture and reuse this.
- Post-Treatment: The clean water gets minerals put back in, its pH adjusted, and disinfected so it’s safe to drink.
- Storage and Distribution: We store the treated water and then send it out to people who need it.
Single-pass systems run seawater through one set of RO membranes. These are the most common for making general drinking water. They’re a good choice if you’re okay with product water having 200-500 ppm TDS. Single-pass systems cost less upfront, use less energy (typically 2.5-4.0 kWh per cubic meter), and are simpler to operate compared to double-pass setups.
ultra-pure water, with TDS below 10 ppm. You’ll need double-pass systems for things like making pharmaceuticals, building semiconductors, boiler feed water, and any other use where the WHO guideline of less than 300 ppm TDS isn’t pure enough. Double-pass systems use more energy, about 3.5-5.5 kWh per cubic meter.
| Feature | Single-Pass SWRO | Double-Pass SWRO |
|---|---|---|
| Product Water TDS | 200-500 ppm | 1-10 ppm |
| Operating Pressure | 800-1,000 psi | 800-1,000 psi (1st) + 150-300 psi (2nd) |
| Energy Consumption | 2.5-4.0 kWh/m- | 3.5-5.5 kWh/m- |
| Salt Rejection | 99.5-99.7% | 99.9%+ |
| Boron Removal | 85-92% | 99%+ |
| Capital Cost | Lower (baseline) | 30-50% higher |
| Best Applications | Potable water, irrigation | Pharmaceutical, industrial, boiler feed |
Key Takeaway: For a town of 1,000 people, you’ll want a system with about 50,000-100,000 GPD capacity. This is based on people using 50-100 gallons of water per day (EPA residential water use estimates). Always add a 15-20% safety margin for when demand spikes.
| System Category | Capacity Range (GPD) | Typical Applications |
|---|---|---|
| Portable / Marine Watermaker | 150-3,000 | Sailboats, yachts, emergency relief |
| Small Commercial | 3,000-20,000 | Small resorts, island communities, remote facilities |
| Mid-Range Commercial | 20,000-100,000 | Hotels, military bases, small municipalities |
| Large Commercial | 100,000-500,000 | Resorts, industrial facilities, large communities |
| Industrial / Municipal | 500,000-10,000,000+ | Municipal water supply, power plants, mining operations |
- Pressure Exchangers (PX): These devices directly move pressure from the salty brine to the incoming feed water. They’re 95-98% efficient. You’ll find them in systems making over 50,000 GPD. Top manufacturers include Energy Recovery Inc. (ERI) and FEDCO.
- Turbochargers: These use the brine’s energy to boost the feed pressure. They’re 80-90% efficient. They’re common in mid-size systems (10,000-100,000 GPD).
- Pelton Turbines: These turn the brine’s hydraulic energy into mechanical energy, helping the high-pressure pump. They’re 85-92% efficient. Good for smaller systems.
- Clark Pump: A piston-like device used in small watermakers (150-1,000 GPD). It’s self-regulating and reliable for boats.
Key Takeaway: For any SWRO system making more than 10,000 GPD, an energy recovery device is a must-have. Pressure exchangers are the most efficient (95-98%) and usually pay for themselves in 12-18 months just from the energy savings. Without an ERD, seawater desalination uses about 6-8 kWh/m-. With a modern ERD, that drops to 2.5-3.5 kWh/m-.
- Intake Screening: Bar screens and traveling screens remove large debris (seaweed, marine organisms). Mesh size: 3-10 mm.
- Coagulation/Flocculation: Ferric chloride or aluminum sulfate dosing aggregates fine suspended particles for easier removal.
- Multimedia Filtration (MMF): Gravity or pressure filters with anthracite, sand, and garnet layers remove suspended solids down to 10-20 microns.
- Ultrafiltration (UF): Membrane-based pretreatment providing consistent 0.01-0.1 micron filtration. Increasingly preferred over conventional MMF for challenging water sources.
- Cartridge Filtration: 5-micron cartridge filters serve as the final safety barrier before the high-pressure pump.
- Chemical Dosing: Antiscalant injection prevents calcium and silica scaling; sodium metabisulfite neutralizes residual chlorine that damages polyamide membranes.
| Parameter | Conventional (MMF) | Ultrafiltration (UF) |
|---|---|---|
| Filtrate SDI | 2.5-4.0 | 1.0-2.5 |
| Turbidity Removal | 90-95% | 99%+ |
| Footprint | Larger | 40-60% smaller |
| Chemical Usage | Higher coagulant demand | Lower coagulant demand |
| Capital Cost | Lower for small systems | Higher initial, lower lifecycle |
| Membrane Protection | Good | Excellent |
| Best For | Clean seawater, beach wells | Challenging source water, algal blooms |
| Source Water | Typical TDS (ppm) | Required Pressure (psi) | Recovery Rate |
|---|---|---|---|
| Baltic Sea | 7,000-10,000 | 400-600 | 50-60% |
| Mediterranean Sea | 38,000-40,000 | 900-1,050 | 35-42% |
| Atlantic Ocean | 33,000-36,000 | 800-950 | 38-45% |
| Pacific Ocean | 33,000-35,000 | 800-950 | 38-45% |
| Red Sea | 40,000-42,000 | 950-1,100 | 33-40% |
| Arabian Gulf | 42,000-48,000 | 1,000-1,200 | 30-38% |
Higher TDS concentrations require higher operating pressures and result in lower recovery rates. Systems designed for Arabian Gulf water, for example, require more robust high-pressure pumps, stronger pressure vessels, and larger pretreatment capacity compared to systems operating on Atlantic Ocean water.
Membrane Type Salt Rejection Flow Rate (GPD) Boron Rejection Best Application Standard SWRO (e.g., Dow SW30HR-380) 99.7% 6,000 91% General seawater desalination High Rejection SWRO 99.8% 5,500 93% High TDS, boron-sensitive applications Low Energy SWRO 99.7% 7,500 90% Energy-sensitive installations High Flow SWRO 99.7% 9,000 89% Maximum production per vessel Anti-fouling SWRO 99.7% 6,500 91% Challenging feed water with organics
| Membrane Type | Salt Rejection | Flow Rate (GPD) | Boron Rejection | Best Application |
|---|---|---|---|---|
| Standard SWRO (e.g., Dow SW30HR-380) | 99.7% | 6,000 | 91% | General seawater desalination |
| High Rejection SWRO | 99.8% | 5,500 | 93% | High TDS, boron-sensitive applications |
| Low Energy SWRO | 99.7% | 7,500 | 90% | Energy-sensitive installations |
| High Flow SWRO | 99.7% | 9,000 | 89% | Maximum production per vessel |
| Anti-fouling SWRO | 99.7% | 6,500 | 91% | Challenging feed water with organics |
Membrane manufacturers such as DuPont (Dow FilmTec), Toray, Hydranautics (Nitto), and LG Chem produce SWRO membranes in standard 8-inch diameter by 40-inch length elements, as well as 4-inch elements for smaller systems. AMPAC USA systems are engineered with premium membranes selected specifically for each application’s feed water characteristics.
| System Capacity (GPD) | Estimated Capital Cost | Energy Cost ($/1,000 gal) | Total Production Cost ($/1,000 gal) | Cost Per Gallon |
|---|---|---|---|---|
| 500 (Marine Watermaker) | $5,000-$12,000 | $12.00-$18.00 | $18.00-$28.00 | $0.018-$0.028 |
| 3,000 | $15,000-$35,000 | $8.00-$14.00 | $14.00-$22.00 | $0.014-$0.022 |
| 10,000 | $45,000-$85,000 | $6.00-$10.00 | $10.00-$16.00 | $0.010-$0.016 |
| 50,000 | $150,000-$350,000 | $4.00-$7.00 | $7.00-$12.00 | $0.007-$0.012 |
| 100,000 | $300,000-$700,000 | $3.50-$6.00 | $6.00-$10.00 | $0.006-$0.010 |
| 500,000 | $1,200,000-$2,500,000 | $2.50-$4.50 | $4.50-$7.50 | $0.0045-$0.0075 |
| 1,000,000+ | $2,000,000-$5,000,000+ | $2.00-$3.50 | $3.50-$6.00 | $0.0035-$0.006 |
Note: Costs based on 2026 market data. Energy costs assume electricity at $0.08-$0.15/kWh. Total production cost includes energy, chemicals, membrane replacement, labor, and maintenance. Actual costs vary by location, feed water quality, and local regulations.
Key Takeaway: The cost per gallon of desalinated seawater ranges from $0.004 to $0.028 depending on system size. Systems above 50,000 GPD with energy recovery devices achieve the most economical production costs of $0.005-$0.012 per gallon. The breakeven point where desalination becomes more economical than water trucking is typically around 5,000-10,000 GPD capacity.
seawater desalination systems and watermakers designed for marine, commercial, industrial, and municipal applications. Systems range from compact 150 GPD marine watermakers to large-scale 600,000+ GPD industrial desalination plants. All AMPAC systems feature premium SWRO membranes, corrosion-resistant 316L stainless steel and duplex stainless steel construction, energy recovery devices (on applicable models), PLC-based automated controls, and comprehensive pretreatment packages.
AMPAC also offers commercial reverse osmosis systems for brackish water applications and industrial RO systems for high-purity water production. Contact AMPAC USA for a custom system quote based on your source water analysis and production requirements.
Seawater desalination system costs range from $5,000 for small marine watermakers (150-500 GPD) to over $2 million for large commercial systems (500,000+ GPD). The cost per gallon of production capacity decreases with system size. A mid-range 50,000 GPD system typically costs $150,000-$350,000 installed, producing water at $0.007-$0.012 per gallon.
Seawater RO systems typically operate at 35-45% recovery rate, meaning 35-45% of the feed water becomes product water and 55-65% is discharged as concentrated brine. Recovery rate depends on feed water TDS, temperature, and membrane configuration. Higher recovery rates increase the risk of membrane scaling and fouling.
Yes, properly desalinated and post-treated seawater is safe to drink and meets WHO drinking water guidelines. SWRO removes 99.5-99.8% of dissolved salts, bacteria, viruses, and contaminants. Post-treatment includes remineralization (adding calcium and magnesium for taste and health), pH adjustment, and disinfection. The WHO recommends a TDS level below 600 ppm for good quality drinking water, and most SWRO systems produce water well below this threshold.
Ready to invest in seawater desalination? AMPAC USA has been manufacturing reverse osmosis and desalination systems for over 20 years, serving customers in 70+ countries worldwide. Browse our complete line of seawater desalination systems and watermakers, or contact our engineering team for a custom system design based on your specific requirements.
Sources: International Desalination Association (IDA), World Health Organization (WHO) Drinking Water Quality Guidelines, U.S. Environmental Protection Agency (EPA), American Water Works Association (AWWA), National Science Foundation (NSF).
Conclusion
This post highlighted how emergency and military-grade water purification systems provide safe drinking water rapidly in the most challenging field conditions. For organizations requiring deployable water treatment capability, AMPAC USA engineers portable and trailer-mounted systems built to perform wherever they are needed. Contact our team at info@ampac1.com or (909) 548-4900 to discuss your emergency water treatment requirements.
Browse AMPAC USA Seawater Systems: Explore our full range of mobile sea water reverse osmosis and seawater desalination systems from portable watermakers to 1,000,000+ GPD land-based plants.
