I have been asked about membrane life by several cruisers planning multi-year trips. How long will a membrane last?
Should we carry a spare membrane?
For lifespan, a well-cared for membrane will typically last 5-7years.
You will never really “wear out” a membrane, since they are rated for continuous operation 24hrs a day for 7 years. Most cruisers will shorten their life due to improper operation and maintenance. Of course, different cruisers have different definitions of “well cared for”, but if you are doing freshwater flushes after each run, don’t let the watermaker sit for more than a week unused without fresh water flushing or pickling, and keep a fresh 5-micron prefilter in place then you are in the top 10% proper maintenance cruisers.
Based on many moons of doing 7-day-a-week watermaker support and service, I don’t recommend carrying a spare membrane. This has a lot to do with how membranes fail. While membranes can suddenly fail, membranes usually don’t fail all at once making 200ppm on Monday then 1000+ on Friday. Their death is usually a slow fade with each season adding another 50-75ppm to the product water quality. This allows for a cruiser paying attention to plan for a membrane change rather than reacting to dead membranes down Island.