Water Maker for Boat
The water maker for boat or as more correctly termed a reverse osmosis (RO) desalination system, allows a sailing boat to produce fresh drinking water from seawater. For cruising yachts operating away from marinas or in remote regions, a water maker significantly extends autonomy, reduces reliance on shore supplies, and improves onboard comfort. Correct installation and operation are essential to ensure reliability, efficiency, and membrane longevity.
Installing a water maker on a boat transforms long voyages by ensuring a steady supply of fresh water. The process begins with selecting a unit sized for your vessel’s power and space, followed by careful installation of intake, filtration, and plumbing systems. Once operational, the water maker converts seawater into potable water through reverse osmosis. Regular maintenance, such as flushing membranes and monitoring filters, keeps performance reliable. With proper setup, a water maker enhances independence, safety, and comfort on extended journeys.
Principles of Water Maker Operation
Marine water makers operate using reverse osmosis, a process in which seawater is pressurized and forced across a semi-permeable membrane. The membrane allows water molecules to pass while rejecting salts, minerals, bacteria, and most contaminants. Typical operating pressures range from 55–65 bar (800–950 psi) for seawater systems. The output is divided into two streams:
- Permeate (product water): low-salinity fresh water
- Brine (reject water): concentrated salt water discharged overboard
Water makers are rated by output, commonly from 20 to 150 liters per hour, depending on vessel size and electrical capacity.
Marine Water Maker System Parts
A typical sailing yacht water maker system consists of:
- Seawater intake and seacock
- Pre-filters, usually a coarse strainer followed by fine sediment filters (20–5 micron)
- High-pressure pump, either belt-driven or electric
- RO membrane housing
- Pressure regulation and control valves
- Salinity (TDS) monitoring
- Fresh water flush system
- Electrical controls and safety interlocks
- Higher-end systems may also include energy recovery devices to reduce power consumption.
Water Maker Installation
Considerations
Location and Layout. Water makers should be installed in a dry, accessible, and well-ventilated area. Common locations include under berths, engine rooms, or dedicated machinery spaces. Adequate space is required for filter changes, membrane servicing, and inspection of hoses and fittings.
Components should be arranged to minimize hose length and avoid tight bends that increase pressure losses. The membrane housing should be mounted securely and horizontally unless specified otherwise by the manufacturer.
Seawater Intake
- The seawater intake must be located below the waterline and away from sources of contamination such as engine cooling outlets, galley drains, or toilet discharges. A dedicated seacock is strongly recommended.
- A sea strainer should be fitted immediately after the intake to prevent debris from damaging the high-pressure pump or clogging pre-filters.
Plumbing and Materials
- All plumbing on the high-pressure side must be rated for RO operating pressures. This typically requires reinforced nylon or stainless-steel fittings and certified high-pressure hose. Standard freshwater hose is unsuitable and unsafe.
- Product water lines should be routed separately from raw water plumbing and discharged initially to a test outlet or drain, not directly into the tank, until water quality is verified.
Electrical Supply
- Electric water makers require careful consideration of the vessel’s battery capacity, charging sources, and wiring. Power consumption varies widely, from 8–10 amps at 12 V for small systems to 40 amps or more for high-output units.
- Heavy-gauge wiring, correct circuit protection, and manufacturer-specified fusing are essential. Many cruising yachts run water makers while the engine is charging or when solar and generator output is available.
Commissioning and Initial Setup
Before producing potable water, the system must be thoroughly flushed to remove preservatives and installation debris. The salinity or TDS meter should be observed closely. Product water should not be directed to the tank until salinity stabilizes within acceptable limits, typically below 500 ppm, and often much lower. During initial startup:
- Inspect all hose connections for leaks
- Verify correct pump rotation and pressure rise
- Flush the membrane according to manufacturer instructions
- Monitor operating pressure and flow rates
Water Maker for Boat Operation
Water makers perform best when operated in clean, open water, ideally offshore and under way. Running the system while sailing reduces fouling and improves intake water quality. Many operators prefer daily runs of 30–90 minutes, which keeps membranes active and reduces biological growth. Key operational practices include:
- Allowing pressure to rise gradually
- Monitoring system pressure and temperature
- Discarding initial product water at startup
- Producing water regularly rather than in long infrequent runs
Fresh Water Flushing and Pickling
After each use, most systems require a fresh water flush, either manual or automatic. This removes salt and organic matter from the membrane, significantly extending its life. If the water maker will not be used for more than a few days, a chemical preservation (pickling) process is required. Pickling solutions inhibit bacterial growth and prevent membrane degradation. Failure to pickle correctly is one of the most common causes of premature membrane failure.
Maintenance and Common Issues
Common operational problems include high operating pressure (often caused by clogged filters), low output (due to fouling or worn pumps), and high salinity readings (indicating membrane damage or leaks). Routine maintenance includes:
- Regular pre-filter replacement
- Inspection of hoses and fittings
- Monitoring pump seals and oil levels (where applicable)
- Periodic membrane cleaning or replacement
Integration with the Fresh Water
System
Product water can be directed to the main tank or to a dedicated water maker tank. Some installations incorporate carbon filters or UV sterilization for additional treatment, though RO water is generally microbiologically safe when produced correctly. Care must be taken to avoid contaminating potable tanks with high-salinity water during startup or system faults.
Water Maker for Boat Summary
A water maker is one of the most transformative systems on a boat. However, it is a complex, high-pressure system that demands careful installation, disciplined operation, and consistent maintenance. When correctly installed and operated, a marine water maker can provide years of reliable service, producing clean, safe drinking water wherever the wind and sea may take the yacht. If you are considering a water maker for boat, make sure you understand all the technical aspects.