Marine Watermakers & DIY Kits

A watermaker is a marine reverse osmosis system that converts seawater to fresh drinking and process water on board vessels and offshore installations. Watermakers use the same RO principle as land-based desalination — high-pressure pumping of seawater through a semi-permeable membrane that rejects salts — but in a compact, marine-rated package. Watermakers eliminate the need for large fresh-water tanks on long-range vessels.

A marine watermaker draws seawater through pre-treatment cartridges, pressurises it with a high-pressure pump, and forces it through a seawater RO membrane that rejects 99.6%+ of dissolved salts. Permeate (fresh water) is collected to the vessel's water tank; concentrate (high-salt reject) returns to the sea. Operating pressure runs 5,500 to 7,000 kPa — substantially higher than brackish water RO — set by seawater osmotic pressure.

Watermaker sizing follows daily water demand and acceptable operating hours per day. A typical cruising couple needs 60 to 80 litres of fresh water per day for drinking, cooking and washing — covered by a 60 LPH watermaker running one hour daily. Larger crews, water-using equipment (showers, dishwashers, washing machines) and longer voyages push capacity requirements higher. Charter and commercial operators typically size watermakers at 250 to 1,000+ LPH.

DIY watermaker kits supply the major components — seawater RO membrane, pressure vessel, high-pressure pump, and pre-treatment — with documentation for owner assembly. The build is suited to experienced sailors and marine engineers comfortable with plumbing layout, electrical connection and pressure system safety. Component performance is identical to complete units; the difference is layout flexibility versus a fixed pre-built footprint.

Marine seawater RO membranes typically last three to seven years depending on use frequency, feed-water quality, and post-shutdown preservation. Membranes left wet and unpreserved between uses degrade rapidly from microbial fouling. Membranes properly preserved with biocide between voyages can last beyond five years on intermittent cruising duty. Replacement is triggered by salt passage rising above the watermaker's design specification, not a fixed time interval.