A watermaker is the one bit of kit that punishes neglect harder than anything else aboard. Leave a winch unserviced and it gets stiff; leave a watermaker membrane to sit wet and idle and it can be ruined inside a fortnight, with a replacement membrane costing roughly twice what cleaning or proper storage would have cost. That asymmetry is the whole reason this article exists. The maintenance is not difficult, but it is unforgiving about timing.
I run a small energy-recovery unit and have kept it healthy through several French seasons, including two winter lay-ups. None of what follows is hard. It is just a set of habits you cannot skip.
Why it needs babysitting
The heart of a reverse-osmosis watermaker is a semi-permeable membrane. Seawater is forced against it under high pressure, water molecules pass through and the salt is rejected. That membrane is a biological surface as far as bacteria and algae are concerned, and warm, still, oxygenated water sitting against it for days is an invitation for them to colonise it. Once they do, output drops, taste goes off, and you are into cleaning or replacement.
The defence is to never let it sit idle and wet for long. The working rule cruisers use: if the unit will be unused for more than about a week, you preserve it.
Flushing versus pickling
Two different jobs, often confused.
A fresh-water flush is the routine you do after every run or before a short layoff. You push unchlorinated fresh water through the system to displace the seawater and stop salt and minor biofilm building up. Many units automate this on a timer. Critically, the flush water must be free of chlorine, because chlorine destroys the membrane on contact, so it is drawn through a carbon filter that strips it out. Replace that carbon flush filter on the maker's schedule, because a tired one passes chlorine straight onto the membrane.
Pickling is the long-term storage job. You circulate a biocide preservative, the classic being sodium metabisulphite, through the system to keep bacteria and algae off the membrane while the boat is laid up. Proprietary storage compounds will hold a membrane safely for up to six months, and some long-term biocide solutions are rated for up to eight months. For a French winter lay-up of five to six months, a single pickle in October will see you through to spring, but check the dates and re-pickle if you overrun.
The consumables you actually replace
A watermaker service is mostly filters and seals.
- The sediment pre-filters, the cartridges that strip particulates before the high-pressure pump, get changed routinely. How often depends entirely on the water you make in. Clean offshore water might give you many weeks; a murky marina or estuary can clog a cartridge in days.
- The carbon flush filter, as above, on schedule.
- High-pressure pump seals and valves, on the manufacturer's hours-based interval, which is a workshop or competent-owner job.
- The membrane itself, only when output or quality has genuinely fallen off despite cleaning. Treated well it lasts years; treated badly it lasts a season.
Keep a logbook of running hours and output in litres per hour at a given pressure. A slow decline in output at constant pressure is the membrane telling you it needs cleaning before it needs replacing.
Sourcing parts in France
This is where a visiting owner can come unstuck. The big marine watermaker brands sold across Europe include Schenker, Spectra, Dessalator, which is itself French, and the Parker and HRO ranges, and France has dealers and distributors for most of them along both coasts. The catch is that filters and chemicals are reasonably easy to find, while membranes and pump rebuild kits for a specific model often have to be ordered in, with a lead time of days to a couple of weeks.
Two practical moves. First, carry your own spares aboard: a set of pre-filters, a spare carbon filter, and enough storage compound for one pickle. These are small, cheap and they let you keep running while a part is shipped. Second, note your exact model and serial number, because watermaker parts are model-specific and a chandlery cannot help you over the phone without them.
If your decision is still whether a watermaker earns its place at all on a French cruise, where the marina tap is rarely far away, the honest argument is laid out in the companion piece on whether you really need a watermaker france. It reaches a more nuanced answer than the brochures.
Reading the warning signs
A watermaker rarely fails all at once. It declines, and if you read the decline you can act before a cheap clean becomes an expensive membrane. Three signals matter. Output dropping at a steady pressure means the membrane is fouling, and a membrane clean with an alkaline then acid solution will usually recover it. Output holding but the water tasting salty, with the salinity meter creeping up, means the membrane is failing or an O-ring is letting raw seawater bypass it, which is a different and more serious fault. And pressure that you cannot reach despite a clean pre-filter often points at the high-pressure pump or a tired pressure regulator rather than the membrane at all.
Most quality units carry a salinity sensor or at least a divert valve so you do not send brackish water to the tank. Trust it. The first slug of water after a layoff or a flush is the one to taste and check, not the water after an hour of running, because a fault shows first in that initial production. I keep a cheap handheld TDS meter aboard as a cross-check, because the day the built-in sensor disagrees with the handheld is the day you learn something is wrong with one of them.
Water you can actually drink
A watermaker makes water that is extremely pure, often purer than the marina tap, but two things still bite cruisers. Reverse-osmosis water is aggressive and slightly low in minerals, which some people dislike the taste of and which can leach from certain tank linings, so many cruisers run it through a simple carbon polishing filter at the galley tap. And the tank itself is the weak link: there is no point making clean water and storing it in a tank with a biofilm in it. Sanitise the fresh-water tank at the start of the season and again mid-season if you store water for long periods in warm weather. The watermaker is only as clean as the tank you put its output into.
Fitting the lay-up routine in
The pickle is just one line on a longer winter list. It sits alongside draining the fresh-water system, antifreezing the engine and pumping out the heads, all covered in the whole-boat guide to winterising boat france. Do the watermaker pickle on the same day you do the rest, label the unit clearly that it is pickled and must be flushed thoroughly before use, and write the date on the log.
That last point catches people out every spring. A freshly pickled membrane is full of biocide and the water it first produces is not drinkable until you have flushed the preservative right out, which can take several tens of litres run to waste. Plan for it. Coming back to commission the boat, you want clean tanks anyway, and the same attention to keeping things dry and mould-free over winter, covered in the article on boat damp mould winter, applies to the watermaker space as much as the cabin.
Get into the rhythm of flush after use, pickle before the long sleep, change the filters on time, and the watermaker quietly becomes the reliable servant it is sold as rather than the expensive heartbreak so many cruisers describe. The difference between those two outcomes is almost entirely the timing of a few simple jobs.
