How often should I service a boat watermaker?
I have a reverse-osmosis watermaker on my cruising yacht and use it most days during summer, then leave it idle between trips. How often should I change filters, flush it and arrange a proper service?
Answer
Check your watermaker every time you run it, service the seawater strainer and prefilters when they become dirty or restrict flow, and follow the maker's fresh-water flushing schedule while it sits idle. There is no single annual service interval for the whole unit: filters, preservation, pump maintenance and membrane cleaning each have different triggers.
Checks before every run
Start with the exact watermaker model, its maintenance instructions and any service records. The equipment manual matters more than the yacht's general handbook because pump designs, flushing arrangements and storage treatments differ, even between installations on the same boat.
Before starting, check that the seawater inlet and discharge valves are open, then inspect the strainer and filters. Avoid making water in muddy or polluted harbours. Contaminated feedwater can foul filters quickly and cause problems that a routine flush will not cure.
- Look for leaks, hose chafe, loose mountings and salt deposits.
- Record product-water output, salinity or total dissolved solids, and the pressure readings your unit provides.
- Compare readings with previous runs in similar seawater temperature and salinity.
- Check that rejected water is diverted correctly before product water reaches the tank.
Cold seawater reduces output, so a winter drop in production does not automatically mean the membrane needs cleaning. On Spectra Clark Pump systems, some crystal formation around the pump blocks is normal. Wipe salt deposits away with a damp cloth and investigate any leakage.
Strainer and prefilter servicing
Inspect the seawater strainer frequently during operation, particularly after entering water containing weed, sediment or plankton. Clean its stainless-steel screen whenever debris accumulates. In difficult conditions, you may need to check it several times during one run.
Switch off and isolate the watermaker, close the inlet seacock and release system pressure before opening strainers, filter housings or pipework.
Service prefilters when the filter-condition indicator shows increasing restriction, feed pressure falls or the manufacturer's specified pressure limit is reached. Do not wait for a calendar date if the machine is struggling for feedwater. A cartridge may last weeks in clear offshore water and clog within hours in dirty coastal water.
Use the specified cartridge rating and arrangement. The Spectra Cape Horn Extreme 330 spares list, for example, specifies 5-micron filters; other installations may use staged filtration. Keep housing seals clean, inspect their condition and check for leaks after reassembly.
For weekend cruising, Spectra's suggested Cape Horn spares include six 5-micron cartridges and one carbon filter. For two to six months aboard, that rises to twelve cartridges and two carbon filters. These quantities guide stocking, rather than set a replacement timetable.