Imagine cruising on your yacht across vast blue waters, free from the constraints of freshwater supply and no longer dependent on marinas. A reliable watermaker (desalination system) can turn this dream into reality. While dock-side freshwater connections remain the most economical option, a watermaker becomes indispensable when exploring remote locations or facing unexpected freshwater shortages.

This comprehensive guide explores every aspect of yacht watermakers, from their working principles to selection criteria, installation techniques, and maintenance practices.

How Watermakers Work: Reverse Osmosis Explained

The core technology behind watermakers is Reverse Osmosis (RO). In simple terms, seawater is forced under high pressure through a specialized RO membrane that acts as an ultra-fine filter. This membrane allows only water molecules to pass while blocking salts, bacteria, viruses, and other impurities. The result is clean, drinkable freshwater.

It's important to note that RO membranes aren't simple filters. They require constant water flow to wash away trapped impurities and prevent clogging. Therefore, watermakers typically have three outlets: freshwater output, concentrated brine discharge, and seawater intake.

Two Main Types of Watermakers

The key difference between watermaker systems lies in how they generate the required high pressure:

High-Pressure Pump Systems

• Directly uses a powerful pump to force seawater through the RO membrane
• Advantages: Fast production (typically 60+ liters/hour)
• Disadvantages: High power consumption (500W+), usually requires generator power
• Simple design with few moving parts makes maintenance easier

Energy Recovery Devices (ERD)

• Uses a low-pressure pump combined with a pressure exchanger (like Clark pump) that transfers pressure from the brine stream to the intake
• Advantages: Energy efficient (12V/9A power, 4-5 watt-hours per liter)
• Disadvantages: Slower production (20-60 liters/hour), more complex design with higher maintenance needs

Choosing Between Systems: Power Supply is Key

The decision largely depends on your yacht's power system. Generator-powered yachts benefit from high-pressure pump systems that can quickly fill water tanks. For vessels relying on solar or wind power, energy recovery systems are more suitable due to their lower power consumption.

Selection Considerations Beyond Price

• Production capacity: Match to your daily water needs (typically 50-100 liters per person per day)
• Size and weight: Compact and lightweight models save valuable space
• Noise levels: Quieter operation enhances onboard comfort
• Maintenance costs: Consider replacement intervals and costs for RO membranes and filters
• After-sales service: Choose reputable brands with good support networks

Installation Best Practices

• Use dedicated through-hull fittings for seawater intake and brine discharge
• Position the intake low enough to avoid air ingestion during heeling
• Avoid turbulent water locations near propellers or rudders
• Install discharge outlets above the waterline
• Mount pumps as low as possible for better pressure generation
• Follow manufacturer recommendations for hose diameters and routing
• Use properly sized wiring to prevent voltage drops

Water Quality Monitoring

Total Dissolved Solids (TDS) meters measure output water purity. Values below 500ppm are safe to drink, with well-maintained systems achieving 200-300ppm. Regular monitoring helps detect pump or membrane issues early.

RO Membrane Maintenance

• Use the system regularly (ideally every few days)
• Flush with fresh water after use (remove chlorine with carbon filters if using tap water)
• For short-term storage (1-5 days), keeping membranes wet with seawater is generally acceptable
• For medium storage (1-2 weeks), fresh water flushing is essential
• For long-term storage (over a month), use propylene glycol preservatives
• Avoid operating in polluted anchorages where waste tanks discharge

Seasonal Maintenance

• 1-5 days: Most systems tolerate this period without special treatment
• 1-2 weeks: Fresh water flushing is mandatory
• Over a month: Requires preservative treatment with manufacturer-approved solutions

For vessels remaining in clean water areas, consider automated periodic flushing systems that run briefly every few days to maintain membrane health.