Watermaker membrane storage and biocide fresh water flush

Reverse osmosis watermaker membranes ($400-1500 each) live or die based on storage protocol. A dry or bacteria-fouled membrane is dead. Rules: (1) IN USE (running regularly): after every session, run a FRESH WATER FLUSH for 5-10 minutes with product water (some units automate this via a solenoid) to purge salt from the membrane. Salt left sitting in the membrane over hours crystallizes into the polyamide layer and reduces capacity permanently. (2) SHORT-TERM IDLE (up to 5 days): the fresh water flush is enough. Salt-free water in the membrane is stable for about a week in most climates. (3) MEDIUM-TERM IDLE (5 days to 3 weeks): pickle with a mild biocide. Sodium metabisulfite at 1 percent concentration is the standard, pump it through the low-pressure side (bypass the membranes) to displace fresh water. The membrane sits in biocide, bacteria can't grow. (4) LONG-TERM IDLE (3 weeks to 12 months): stronger pickling with propylene glycol plus biocide, or SW-30 / Sea Recovery preservative solution. Renew the pickle every 6-12 months for storage over a season. (5) NEVER STORE DRY. A dry membrane cracks the thin-film composite and the unit produces salty water forever after. Symptoms of membrane damage: high salinity output (over 500 ppm on a normal-charge unit that should produce under 300), high pressure needed for normal flow (the membrane is fouling), and product water taste of chlorine or bleach if you used the wrong preservative. Rinse the pickle out thoroughly before returning to service, run water to drain for 30 minutes before drinking.