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Solved problems · Watermaker · Crew answer

Why is my watermaker making less water than it used to?

Low watermaker output usually comes from clogged prefilters, an intake air leak, colder seawater or a fouled membrane. Check flow and filters first; clean the membrane only per the maker's procedure.

Symptom

Product water flow is noticeably lower than when the unit was new, run times are longer, and sometimes the salinity (ppm) reading rises or the unit alarms.

Likely cause

A clogged sea strainer or prefilters starve the high-pressure pump, and an air leak in the feed line does the same. Colder seawater lowers the output of every reverse-osmosis unit. Over time, biological growth or mineral scale on the membrane cuts flow and raises salinity.

Stop now if

Pressure goes above the maker's maximum, a high-pressure hose or fitting weeps, or the product water tastes salty or smells. Shut down, relieve the pressure before opening anything, and don't send questionable water to the tanks.

Protect the membrane and yourself

Never let chlorinated dock water reach the membrane; fresh-flush through the maker's carbon filter. Wear gloves and eye protection with cleaning chemicals.

The fix, in short

  1. Change the prefilters and clean the strainer. Replace the prefilter elements and clean the sea strainer. Filters that clog quickly mean dirty feed water; avoid making water in harbors, rivers or murky water.

  2. Check for air in the feed line. Look for bubbles in the filter housings or the product water, and tighten fittings and housing seals. Air reduces output and can damage high-pressure pumps.

  3. Allow for seawater temperature. Expect less water in cold seawater and compare with the maker's temperature chart before suspecting a fault. Never raise operating pressure above the maker's maximum to make up for it.

  4. Check product salinity and the meter. Divert product water when salinity is high, and check the salinity probe against a handheld TDS meter.

  5. Clean or replace the membrane per the manual. If flow is still low with clean filters and normal pressure, the membrane is probably fouled. Clean it with the maker's chemicals in the order specified. If salinity stays high after cleaning, it may need replacing. Fresh-flush or pickle the unit whenever it sits.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Watermaker: Reverse-osmosis desalinator, 12 V DC or engine-driven
  • Filtration: Sea strainer and prefilters

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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