Filter changes, checks and preventive maintenance

Maintaining a boat watermaker is crucial to ensuring optimal and long-lasting performance. The watermaker is a complex system relying on sensitive components: a high-pressure pump, a reverse osmosis membrane, pre-filters, check valves, and other valves, each playing a specific role in producing potable water.

The main objective of maintenance is to ensure a consistent production of high-quality fresh water, free from contamination and altered taste. A poorly maintained watermaker can produce insufficiently purified water containing particles, salt, or even bacteria, posing a health risk to the boat's occupants.

Another key objective is to preserve the lifespan of the components. The reverse osmosis membrane, for example, is expensive and highly sensitive to chlorine, limescale deposits, organic matter, and pressure fluctuations. Pre-filters protect the membrane and pump from abrasive particles; if they are not replaced regularly, they become clogged, leading to a drop in pressure, increased energy consumption, and even premature membrane failure.

Regular maintenance also helps prevent breakdowns and emergency interventions at sea. Properly maintained equipment operates reliably and helps avoid situations where potable water runs out while underway. This includes checking the tightness of fittings and pipes, verifying the operation of valves and pumps, and monitoring the flow rate and conductivity of the water produced.

Finally, maintenance helps maintain the system's energy efficiency. A properly functioning pump and clean filters ensure that the watermaker consumes as little energy as possible to produce the maximum amount of water. This is especially important on a boat, where energy is limited and often expensive to produce.

Neglected maintenance can lead to:

A decrease in water flow or quality,
Premature wear of the membrane,
A costly breakdown or contamination of the circuit.

Consumable parts to be replaced

Pre-filters: These filters remove sand, sediment, and particles that would otherwise protect the pump and diaphragm. If they become clogged, the available pressure drops and the diaphragm wears out faster. Filters are the first line of defense; neglecting them allows large debris to reach sensitive components.

Replace cartridges according to usage (typically every 20–50 h) or as soon as the pressure differential increases.
Have at least 2 sets of spare filters on board.
Never run the desalination unit without filters in place.

Activated carbon (if present) : Carbon removes chlorine and certain organic compounds that could damage the membrane or alter the taste of the water. Chlorine, even in low concentrations, destroys the reverse osmosis membrane very quickly.

Replace the charcoal bed every 6–12 months depending on usage and water quality.
Check that the charcoal is not saturated (odor, taste, performance).
Do not rinse the circuit with chlorinated water without having neutralized the chlorine.

Reverse osmosis membrane : The membrane is the central component that separates salt and impurities. It is also the most expensive. Its lifespan depends heavily on the quality of the pre-filters, the absence of chlorine, and chemical maintenance. A contaminated membrane (biofilm, precipitates) will experience a drop in production and rejection capacity.

Monitor the salinity/conductivity of the water produced regularly.
Replace the membrane every 3–5 years or as soon as performance drops.
In case of confirmed contamination, remove and clean/replace the membrane according to manufacturer's recommendations.

High-pressure pump

The high-pressure pump is vital for achieving the pressure required for reverse osmosis. A failing pump will cause a drop in production or a complete breakdown. Unusual noises, vibrations, and leaks indicate wear and tear.

Checks/actions:
Listen to the pump (noise, vibrations).
Control leaks around the body and connections.
Check the temperature after prolonged operation.
Replace worn seals and bushings.

Feed/priming pump

The feed pump ensures the delivery of seawater without cavitation. Air in the circuit prevents the pump from functioning correctly and can damage the diaphragm.

Checks/actions:
Check for the absence of air in the circuit (bleed if necessary).
Make sure the intake is not blocked (grilles, valves).
Check the tightness of the intake fittings.

Operating pressure

The operating pressure (often 55–65 bar depending on the model) is what allows the membrane to separate the fresh water from the salt discharge. Too low a pressure reduces production; too high a pressure risks damaging the membrane or the pump.

Checks/actions:
Read the pressure reading at each start-up.
Adjust according to the ranges recommended by the manufacturer.
Investigate causes of pressure loss (clogged filters, weak pump).

Pipes and fittings

Leaks or loose clamps cause pressure loss, air ingress, or salt water seepage into sensitive areas. Corrosion of the fittings can lead to rupture.

Checks/actions:
Monthly visual inspection of pipes, clamps and fittings.
Tighten or replace corroded clamps.
Replace stiff, cracked or salty pipes.

Flow rate and conductivity of the water produced

The flow rate indicates production; the conductivity (or salinity) indicates quality. High conductivity means a faulty membrane, poor rinsing, or insufficient pressure.

Checks/actions:
Measure the flow rate and note the value.
Measure the conductivity or salinity using a TDS/cond. Compare to the manufacturer's reference values.
If there is a discrepancy, check the filters, pressure, and diaphragm.

Electricity and fuses

An unstable power supply or loose connections can cause power surges, power loss, or fire hazards. An undersized fuse may mask an underlying electrical problem.

Checks/actions:
Check the power supply voltage and the condition of the fuses.
Check wiring (oxidation, overheated connectors).
Check grounding and protective devices.

Valves and check valves

They regulate the flow and prevent the backflow of salt water into the fresh water system. A faulty valve can contaminate the drinking water supply.

Checks/actions:
Manually test the opening/closing of the valves.
Check the non-return valves by looking for backflow.
Replace valves that leak or stick.

Cleaning/rinsing chemicals

The products (acids for limescale, alkalis for organic matter) are used to descale and decontaminate the membrane. Incorrect use (dose, timing) can damage the components.

Checks/actions:
Check expiry dates and seals.
Ensure compatibility with the system materials.
Store in a dry, ventilated place, separate from food.

Before each sailing trip

Before each sailing trip

A pre-departure check prevents you from being at sea without water or with a faulty device. It's the last opportunity to easily resolve a problem.

Concrete actions:
Check pre-filters and change if dirty.
Perform a short production cycle to check flow rate and conductivity.
Check for leaks in the system.

During the season / regular use

Frequent use without rinsing promotes the accumulation of deposits or biofilm. Regular rinsing keeps the membrane clean.

Concrete actions:
Rinse with fresh water after each prolonged production.
If inactivity >72 h, start a storage rinse cycle.
Note the hours of use to anticipate filter changes.

Every year

The annual maintenance is a complete overhaul to prevent major failures: chemical cleaning, preventive replacement of consumables and overall testing.

Concrete actions:
Replace all filters (pre- and carbon if present).
Perform chemical cleaning (acidic then alkaline procedure) according to manufacturer's recommendations.
Check and, if necessary, replace the membrane.
Check hoses, valves, fittings and grease seals.
Test pressure, flow rate and conductivity and record the values.

In conclusion: Essential tips for longevity

Never use chlorinated water for rinsing
Why: Chlorine destroys the membrane in a very short time.
Action to take: Always use fresh, non-chlorinated water; if the drinking water on board is chlorinated, neutralize the chlorine before rinsing.

Rinse with fresh water after use

Why: Eliminates salt and residues that form deposits and promote corrosion.
Action: Run an immediate rinse cycle after production, especially before a shutdown period.

Use the desalination plant regularly

Why: Inactivity promotes bacterial growth and biofilm formation.
To do: Operate the device at least once a week if possible, or perform a storage rinse.

Monitor the quality of the water produced

Why: Conductivity or a salty taste are the first signs of membrane degradation.
Action: Measure conductivity and note the change; if there is an increase, diagnose immediately.

Store membranes properly during extended periods of inactivity.

Why: Membranes need to remain moist and protected against microbial growth.
To do: Use a preservative solution recommended by the manufacturer.

Keep a maintenance log

Why: Trace of interventions, useful for diagnosis and resale.
To do: Record dates, operating times, parts changed, test values.