Your yacht watermaker stopped producing — or it's making water that tastes wrong, reads high on the TDS meter, or trickles out at half the normal rate. A systematic check tells you whether it's a quick fix or a job for a specialist. This guide covers low flow, high salinity, won't start, bad taste or odor, pressure problems, and brand-specific notes.
Low flow is the most common complaint, and clogged pre-filters cause most of it. A system that once made 15 GPH now struggles to hit 8. Work through these five checks in order.
A dirty 5-micron sediment filter starves the high-pressure pump of feed water. Change sediment pre-filters every 200-300 hours of runtime or any time flow drops unexpectedly.
Cold water is harder to push through the membrane. A system calibrated in San Diego summer water (65-70°F) can lose 15-20% of rated output in winter or colder latitudes. That's physics, not a malfunction.
Worn piston seals or ceramics reduce pressure and cut flow proportionally. If your high-pressure gauge reads below normal (typically 800-900 PSI for a standard RO membrane), the pump is the likely culprit. See pump repair.
| Symptom | Most likely cause |
|---|---|
| Low flow, normal pressure | Clogged pre-filter or cold water |
| Low flow, low pressure | Pump wear or pressure regulator issue |
| Low flow, normal pressure, high salinity | Membrane fouling or O-ring leak |
| Flow dropped suddenly | Air ingestion, burst pre-filter, or pump failure |
| Flow declined gradually over weeks | Membrane aging or progressive bio-fouling |
A stuck or miscalibrated regulator can stop the system reaching operating pressure. If pressure is low and the pump checks out, adjust the regulator in small steps while watching the gauge.
Membranes last roughly 3-5 years under normal use. Fouled or aged membranes produce less flow and pass more salt; replacement is often the most cost-effective fix at this stage. See membrane replacement and the low-flow deep dive.
Product water should read below 500 ppm TDS, ideally below 200 ppm. Anything above 1,000 ppm is a red flag — stop using it for drinking and cooking until the source is found.
Degraded or dislodged end-cap O-rings let brine bypass the membrane into the product stream. Pull the end caps, replace the O-rings, and re-seat the membrane — a job most experienced owners can handle with the right kit for their vessel size (2540, 4040, or 2521).
Check the controller for fault codes before touching anything mechanical. Most modern units will refuse to start if a sensor is out of range.
Odor is almost always biological or chemical, not a membrane failure — and most common after a period of inactivity.
A system left unpickled for more than a few weeks can grow microbes in the membrane and pressure vessel, producing a musty or sulfurous smell. Flush thoroughly; advanced cases need a low- or high-pH membrane cleaning. Prevent it by pickling with sodium metabisulfite whenever the unit will sit idle more than two weeks.
An exhausted carbon block passes chlorine and organics. If you flush with treated dock water, carbon life is shorter than you'd expect — replace it.
| Odor type | Likely source |
|---|---|
| Musty / earthy | Bio-fouling in membrane or pressure vessel |
| Chlorine / chemical | Exhausted carbon block passing chlorine |
| Sulfurous / rotten egg | Bacterial growth in product tank or hose |
| Plastic / solvent | New hose off-gassing, or wrong hose material |
If the smell comes from the tank rather than the watermaker output, check the tank, vent, and hose material before blaming the watermaker.
Sea Recovery: robust workhorses. Common issues are high-pressure pump seal wear (the pump is rebuildable) and control board failures on older units. If it trips the breaker on startup, check for pump seizure first.
Spectra: the Clark pump is efficient but adds a failure point — output drops while power draw rises. Controllers also throw sensor faults without a true mechanical failure; check sensor connections before ordering parts.
Village Marine: built for high duty cycles. On recreational boats the main failure is neglect — membrane fouling from inactivity.
FCI: modular and easy to service. Pre-filter housings and fittings are a known weak point — check for cracks or weeping.
HRO: high-output systems on larger yachts. Seal kits and membranes can have long lead times — plan ahead before departing for Mexico.
If replacing a consumable (filter, O-ring, membrane) fixes it and you have the parts, go ahead. If the problem is in the pump, electrical system, or pressure circuit, the risk outweighs the cost of a service call.
Low flow is most often caused by clogged pre-filters or a dirty sea strainer. Other causes, in diagnostic order, are cold feed water (15-20% less output), high-pressure pump wear, a stuck pressure regulator, and an aged or fouled RO membrane.
Product water from a healthy marine RO system should read below 500 ppm TDS, ideally below 200 ppm. Above 1,000 ppm is a red flag; stop drinking the water until the cause is found.
Failed or dislodged pressure vessel end-cap O-rings, which let brine bypass the membrane. Other causes include a damaged product-water tube, an end-of-life membrane, running below about 600 PSI, or a drifting salinity probe.
Usually bio-fouling after the system sat without pickling, or an exhausted carbon block passing chlorine or organics. Sulfur smells often come from bacteria in the tank or hoses rather than the watermaker itself.
A standard seawater RO membrane typically runs at 800-900 PSI. A reading well below your normal operating pressure points to pump wear or a pressure regulator problem.
Pickle the system with a food-safe preservative such as sodium metabisulfite any time it will sit idle for more than two weeks.
Send your system make, model, symptoms, and your pressure and salinity readings if you have them. We cover Shelter Island, Point Loma, Harbor Island, and greater San Diego, plus select Baja and Mexico travel jobs — most repairs happen at the slip.