AMPAC builds seawater reverse osmosis systems from 100 GPD to 100,000 GPD – portable emergency units you can carry, skid-mounted land-based plants, containerized mobile systems, and Class 1 Division 2 offshore units. Below: how seawater RO differs from every other kind of water treatment, how to size a system, what it costs to run, and which AMPAC model range fits your application.
What makes seawater desalination different from ordinary reverse osmosis?
Pressure. Ordinary tap or brackish water RO runs at roughly 150-250 PSI. Seawater at 35,000 mg/L TDS has an osmotic pressure of around 350 PSI before you have moved a single drop through the membrane, so seawater systems operate at 800-1,200 PSI. That number sets the pump, the pressure vessels, the piping alloys, the membrane chemistry, and the energy bill.
The second difference is recovery. A brackish system might recover 75% of its feed as product water. A seawater system typically recovers 30-45%, because pushing further concentrates the brine to the point where scaling and osmotic pressure make the economics turn against you. Plan for the majority of your intake to leave as concentrate.
The third is materials. Seawater and 316 stainless steel do not get along indefinitely. High-pressure wetted components are specified in duplex stainless or super duplex, and corrosion allowance is a design decision rather than an afterthought.
For the full technical walk-through, see how reverse osmosis converts ocean water to drinking water.
How do I size a seawater desalination system?
Start from daily demand, not peak flow. A system rated at 6,000 GPD produces that over 24 hours of running – 250 gallons an hour – so if your demand is 6,000 gallons concentrated into an eight-hour window, you need either a larger system or storage. Storage is almost always cheaper than steel.
Then account for three things that reduce output in service:
- Temperature. Membrane flux falls with colder feed water. A system sized on 25 °C specs will underproduce in a 12 °C winter sea.
- Membrane age. Output declines over a membrane’s service life. Sizing with no margin means the system is undersized by year three.
- Downtime. Cleaning, filter changes, and service all take the plant offline. If continuity matters, that is an argument for two smaller trains rather than one large one – which is exactly what the twin redundant 2 × 2,000 GPD configuration exists for.
You can work through the numbers yourself with the AMPAC RO system calculators, which cover design inputs, stream data, recovery, concentrate chemistry, and a scaling index.
Which AMPAC seawater system fits my application?
| Range | Capacity | Typical use |
|---|---|---|
| Portable and emergency | 100-300 GPD | Disaster relief, small vessels, field deployment |
| Compact watermakers | 600-1,000 GPD | Yachts, small crews, remote cabins |
| Mid-range watermakers | 1,500-6,000 GPD | Commercial vessels, small resorts, island homes |
| LX land-based skids | SW1500-LX to SW12000-LX | Hotels, clinics, small communities |
| Large LX plants | SW20K-LX to SW100K-LX | Municipal supply, industrial process water |
| LXC mobile plants | SW80K-LXC, SW100K-LXC | Containerized, relocatable, rapid deployment |
| Offshore C1D2 | SW10K-C1D2, SW20K-Class1-Div2 | Hazardous-area platforms and rigs |
| ROWPU | SW4500 | Military field water purification |
Browse the complete range in seawater desalination systems.
What does seawater desalination actually cost to run?
Buyers ask about capital cost. Energy is what decides the project. Seawater RO’s operating cost is dominated by the high-pressure pump, which is why energy recovery devices matter at larger scales and why solar becomes attractive where diesel has to be shipped in.
Membrane replacement, cartridge filters, cleaning chemicals, and labor make up the rest. All of it recurs. A plant specified purely on purchase price tends to be the expensive one by year five.
The full breakdown is in the true cost of desalination: CAPEX, OPEX, and ROI.
Why boron gets its own conversation
Boron is the one seawater contaminant that single-pass RO struggles with. It passes through membranes as uncharged boric acid at natural seawater pH, so where a permeate specification sets a tight boron limit, meeting it usually means a second pass, pH elevation, or a boron-rejection membrane. Limits vary by jurisdiction and by end use – irrigation water for boron-sensitive crops is often stricter than drinking water. If boron appears in your specification at all, it changes the system design: see boron removal in seawater desalination.
Off-grid, island, and remote applications
Desalination is worth most where infrastructure is weakest. Those are also the places where power is least reliable. Two situations come up repeatedly:
- Island communities, where the alternative is shipped or barged water at a cost that makes a desalination plant pay for itself quickly.
- Solar-powered desalination, where the design question shifts from “how much water” to “how much water per available kilowatt-hour, and what happens at night”.
Marine, military, and offshore
Shipboard and military watermakers face constraints a shore plant does not: footprint, motion, shock, intermittent duty, and crews who need to service the unit without a factory technician. AMPAC’s comparison of military and marine watermaker manufacturers sets the AMPAC range against Parker (Sea Recovery) and Veolia on those terms. For an overview of the marine range itself, see seawater desalination watermakers for marine, military and offshore use.
Brackish water needs a different system
If your feed is a brackish well or inland aquifer rather than open ocean, you do not need a seawater system, and buying one wastes both capital and energy. Brackish RO runs at lower pressure with higher recovery. Inland brackish sources are an underused resource across the western United States – see brackish water desalination in Utah and the western US – and AMPAC builds for that feed water separately under brackish water RO.
Frequently asked questions
How much seawater does a desalination system need to produce one gallon of drinking water?
At a typical seawater recovery of 30-45%, roughly two to three gallons of seawater per gallon of product water. The remainder leaves as concentrate. This is why intake and discharge design matter as much as the RO skid itself.
Can a seawater system run on brackish water?
Physically yes, economically no. A seawater system on brackish feed runs its high-pressure pump far harder than the application requires, burning energy you do not need to spend. Match the system to the feed water.
What is the smallest practical seawater desalination system?
AMPAC’s range starts at 100 GPD, with a 150 GPD portable emergency unit designed to be transported and deployed by hand for disaster relief and field use.
How long do seawater RO membranes last?
Service life depends on feed water quality, pretreatment, cleaning discipline, and how hard the system is driven. Good pretreatment is the single largest factor – most premature membrane failure traces back to fouling that pretreatment should have caught.
Does AMPAC ship desalination systems internationally?
Yes. AMPAC has delivered water treatment systems to customers in over 120 countries, engineered and assembled in Woods Cross, Utah.
How do I get a system specified for my site?
Send your feed water analysis, daily demand, and permeate specification. Call (385) 530-1026 or use the request a quote form, and AMPAC’s engineering team will size the system against your actual conditions rather than a catalog assumption.