Why Ships Need Their Own Water Supply for Naval Missions

Fresh water is the biggest hurdle for naval operations. Any ship carrying a limited amount of drinking water has to return to port, or meet up with a supply ship, as soon as that water runs out. For fast patrol vessels and smaller combat ships, this dependency can limit how far they can go to just a few days of travel. It basically ties the fleet to its home base.

This really impacts how a navy operates. A patrol ship that has to come back to port every three days for water spends a lot of its mission time just traveling, not actually on station. The costs, for fuel, for crew time, for less surveillance coverage, add up fast across a whole fleet. For navies working in areas with long coastlines or contested waters, this reliance on resupply is a real weak spot.

The fix? It’s been around for a while in ship design: making water right on the ship. A vessel with a specially designed seawater reverse osmosis (SWRO) watermaker can constantly make fresh drinking water from the ocean around it. This makes the ship water-independent for as long as it has fuel, food, and its crew is ready. Global Water Intelligence says marine watermakers are now standard on almost all major naval combat ships and more and more patrol and auxiliary vessels worldwide are getting them installed.

What the South Korean Navy Needed, and How AMPAC USA Delivered

The Republic of Korea Navy has a fleet of patrol vessels. They watch over South Korean territorial waters, the demilitarized zone sea boundary, and the wider Yellow Sea and Sea of Japan. These ships work in tough conditions and need to stay on patrol for long stretches without shore support.

Their water needs were clear: each vessel needed a watermaker big enough to provide all the daily drinking, cooking, and hygiene water for the full crew, indefinitely. Their old setup, where ships could only stay at sea for three days before needing water, was holding them back. The goal after AMPAC USA installed our watermakers was at least 30 days of endurance, a ten-fold improvement.

AMPAC USA custom-built seawater desalination systems for each type of patrol ship. Each watermaker takes raw seawater, which usually has about 35,000 parts per million (ppm) of dissolved solids, and turns it into drinking water. This new water meets World Health Organization and Korean military standards. The finished water has less than 500 ppm of dissolved solids, rejects over 99.4% of salt, and is safe for all uses on board without any extra treatment.

How Military Seawater Desalination Watermakers Work

A naval seawater reverse osmosis system isn’t like a commercial marine watermaker in a few key ways. It has to run reliably in conditions with lots of vibration, salty air, extreme temperatures, and power changes. And it must keep working through things that would make a commercial system shut down.

Getting Water In and Pre-Treatment

Seawater comes from the ship’s sea chest, an intake fitting below the waterline. It then goes through several pre-treatment steps. This usually means coarse straining to remove big particles, sediment filtration, and adding anti-scalant chemicals. These chemicals stop minerals from building up on the RO membranes. Sometimes, a media filter with anthracite or other materials further reduces cloudiness before the water hits the membranes.

High-Pressure Pumping

Seawater reverse osmosis needs operating pressures between 800–1,200 psi (55–83 bar). That’s to overcome the natural osmotic pressure of seawater and push water molecules through the semi-permeable membranes. Military-grade high-pressure pumps are built for continuous work at these pressures with very little maintenance. They use materials that stand up to seawater corrosion: duplex stainless steel, titanium, and high-performance polymer parts.

The RO Membrane Stage

At the core of the system is the RO membrane array. Here, pressurized seawater touches spiral-wound semi-permeable membranes. These membranes let water molecules pass through, but they block salt ions, bacteria, viruses, and all other dissolved and suspended contaminants. The clean water stream, called permeate, comes out at low pressure as fresh water. The waste stream, called brine, contains the concentrated salts and goes back overboard. A well-designed SWRO system typically turns 30–40% of the incoming water into clean product, with the rest discharged as brine.

Energy Recovery

The high-pressure waste brine still has a lot of hydraulic energy. Advanced SWRO systems include energy recovery devices (ERDs), like pressure exchangers or Pelton wheel turbines. These devices capture some of that energy and send it back to the feed pump. This cuts overall power use by 30–50% compared to systems without recovery. For ships with limited generator capacity, saving energy isn’t just about cost, it’s essential for operations.

Post-Treatment and Remineralization

RO product water has very few minerals and is slightly acidic. To meet drinking water standards and stop corrosion in the ship’s pipes, post-treatment usually involves a calcite contactor or carefully adding calcium and bicarbonate. This raises the pH and hardness to acceptable levels. Then, final disinfection with chlorine or UV keeps the water microbiologically safe in the storage and distribution system. Who wants rusty pipes, right?

AMPAC USA’s Experience with Military and Naval Watermakers

AMPAC USA has provided watermakers to naval and military clients on many continents. We’ve worked on U.S. military contracts, systems for allied foreign navies, and deployments in some of the world’s toughest operational places. We build every system under our ISO 9001:2015 quality management system. This ensures consistent design, production, and testing standards across all the systems we deliver.

What makes AMPAC USA military-grade watermakers different?

• Military specification compliance: Systems are designed to relevant MIL-SPEC standards for vibration, shock, corrosion resistance, and electromagnetic compatibility (EMC)
• Compact, space-optimized design: Naval vessels have strict space and weight budgets. AMPAC USA engineers systems to the smallest possible footprint while maintaining full redundancy for critical components
• Simplified maintenance: Watermaker systems on patrol vessels are maintained by ship’s crew, not specialist technicians. AMPAC USA designs for intuitive operation and maintenance with minimal special tools
• Spare parts logistics support: Global supply chain and in-country support agreements ensure that spare parts are available wherever vessels operate
• Warranty and lifecycle support: Full system warranty and planned maintenance support extending through the intended service life of the vessel

Comparison: Watermaker Technologies for Naval Applications

Operational Impact: From 3-Day to 30-Day Endurance

The operational significance of extending water endurance from 3 to 30 days cannot be overstated in naval planning terms. A patrol vessel on a 30-day independent deployment mission can cover vastly more ocean area, maintain sustained presence in distant patrol zones, and respond to developing situations without being constrained by the logistical clock.

Consider the arithmetic: a patrol fleet of 10 vessels, each requiring a water resupply run every 3 days, must dedicate a significant portion of its collective operating hours to transit between patrol station and port. If the average round-trip transit takes 12 hours, and each vessel must transit twice per week, the fleet loses 24 vessel-hours per week — or more than 1,200 vessel-hours per year — purely to water logistics. Multiply by fuel costs for high-speed transit and the economics of onboard water generation become immediately compelling, quite apart from the operational benefits.

With AMPAC USA watermakers installed, each vessel in the South Korean Navy patrol fleet became genuinely water-independent. Mission planning is no longer constrained by the water clock. Patrol zones can be assigned based on strategic need rather than logistical proximity to resupply. Emergency response capability is extended to the full range of the vessel’s fuel endurance.

AMPAC USA’s Global Naval and Military Track Record

The South Korean Navy contract is one of many military and naval projects completed by AMPAC USA since 1989. Our watermakers and water purification systems have been deployed on naval vessels in Asia, the Middle East, South America, and Europe, as well as on U.S. military forward operating bases and expeditionary installations where no local water supply is available.

For civilian maritime applications, AMPAC USA manufactures a full range of seawater desalination systems for commercial vessels, island communities, coastal resorts, and offshore platforms. The same engineering disciplines that produce military-grade reliability translate directly to demanding civilian applications where downtime is costly and technical support may be far away.

Beyond marine applications, AMPAC USA’s water treatment expertise extends to brackish water desalination, industrial process water treatment, and chiller makeup water systems. Contact our engineering team to discuss naval, maritime, or remote-deployment water treatment requirements. Explore our full range of water treatment systems and learn more about AMPAC USA.

Frequently Asked Questions: Navy and Military Seawater Desalination Watermakers

How much fresh water can a naval seawater watermaker produce per day?

The production capacity of a naval seawater watermaker is sized to the specific vessel’s crew complement, mission duration, and space/power constraints. As a general rule, naval planning allocates 5–10 liters per person per day for drinking water alone, and 30–100 liters per person per day for all potable uses including cooking, hygiene, and galley operations. A patrol vessel with a crew of 40 might require 1,500–4,000 liters (400–1,050 gallons) per day of potable production. AMPAC USA designs systems across a wide capacity range — from 200 GPD compact units for small patrol craft to 50,000+ GPD systems for large surface combatants — matching production to the specific vessel’s requirements. See our reverse osmosis systems page for available capacity configurations.

What is the energy consumption of a seawater desalination system on a patrol vessel?

Modern seawater RO systems equipped with energy recovery devices (ERDs) consume approximately 2–4 kilowatt-hours per cubic meter (kWh/m³) of fresh water produced — a significant reduction from earlier-generation systems that required 6–10 kWh/m³. For a patrol vessel producing 2 m³/day of fresh water, this translates to 4–8 kW of continuous power draw from the vessel’s generators — a relatively modest load that most small combatants can accommodate. Without energy recovery, consumption roughly doubles. AMPAC USA incorporates ERDs as standard in seawater systems above a threshold production rate where the capital cost of the ERD is justified by the operating savings over the system’s service life.

How durable are the RO membranes in a marine saltwater environment?

RO membranes used in seawater desalination are manufactured from thin-film composite (TFC) polyamide material specifically engineered for high-salinity, high-pressure seawater operation. Under properly controlled feed water conditions — adequate pre-treatment, stable pH, controlled temperature — SWRO membranes typically achieve a service life of 3–7 years in continuous operation. Military-grade applications include design features that extend membrane life: conservative flux rates (lower water production per unit of membrane area), thorough pre-treatment, and automated cleaning-in-place (CIP) cycles that restore performance when fouling is detected. AMPAC USA provides replacement membranes and CIP chemicals as part of its lifecycle support programs for naval clients.

Can seawater watermakers operate in polluted or coastal waters?

Coastal and harbor waters present a more challenging feed water profile than open ocean water, with elevated turbidity, biological load, organic contamination, and potentially hydrocarbon contamination near ports. Naval vessels most often operate their watermakers during open-ocean transits rather than in port, and the pre-treatment systems are designed to handle the higher fouling potential of coastal water for short periods. However, heavily polluted water — particularly water with hydrocarbon contamination from fuel or oil spills — requires specialized pre-treatment or, in extreme cases, the watermaker should not be operated until the vessel clears the contaminated zone. AMPAC USA designs pre-treatment systems specific to the vessel’s operating theater, accounting for the typical water quality of the waters where the vessel will spend the majority of its operational time.

How does AMPAC USA support naval clients in foreign countries?

AMPAC USA provides international support through a combination of in-country service partners, direct technical support from our U.S. facility, remote diagnostics via satellite or internet connectivity, and pre-stocked spare parts programs that maintain critical consumables at the client’s naval base. For new contracts with foreign navies, AMPAC USA’s engineering team works directly with the procuring authority to ensure that local technical personnel are trained to the required standard during system commissioning. We provide documentation in the client’s language and can tailor training programs to the maintenance capability of the vessel’s engineering complement. Since 1989, AMPAC USA has supported international customers in over 40 countries across varying infrastructure and logistics environments.

What certifications do AMPAC USA naval watermakers meet?

AMPAC USA designs and manufactures all systems under an ISO 9001:2015 certified quality management system, which governs design control, materials procurement, manufacturing processes, factory acceptance testing, and post-delivery support. Naval systems are designed to meet applicable military standards (MIL-SPEC) for the procuring nation, including vibration and shock resistance, corrosion protection, EMC compatibility, and potable water quality. Water quality from AMPAC USA seawater watermakers meets or exceeds WHO Guidelines for Drinking Water Quality, U.S. military field water standards (FM 10-52), and the applicable national standards of client navies. Systems can be factory acceptance tested to client-specified procedures before shipment, and commissioning tests are conducted to verify performance to specification at the time of installation.

Are seawater desalination systems available for non-military maritime applications?

Yes. AMPAC USA manufactures seawater desalination systems for a full range of maritime and coastal applications beyond naval use. These include commercial fishing vessels, passenger cruise and ferry vessels, offshore oil and gas platforms, remote island communities, coastal resorts and hotels, coastal industrial facilities, and desalination systems for island municipalities. The same engineering competencies that qualify AMPAC USA for demanding naval contracts translate directly to reliability and performance in these commercial contexts. For island water supply and coastal community desalination, see our seawater desalination applications page. For offshore and maritime applications, contact our engineering team with your production requirement and feed water salinity.