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I was looking into portable desalination hand pumps. and I found this one one Amazon for $959 it says

the Katadyn Survivor 06 is the world's smallest hand-operated desalinator and can easily fit into an emergency kit. It removes bacteria, viruses and other contaminants, and can make 1 ounce of drinking water in less than two minutes (nearly 2 pints per hour) with an average pump rate of 40 strokes per minute. This compact, lightweight unit is designed for one to two person use in liferafts or a ditch bag. It's a trusted device used by the US Navy, US Coast Guard, US Air Force and is essential equipment for any offshore cruising vessel.

In separate area it says

enough for a life raft with up to 1-6 people

Probably great for the first day or two, but I would expect that filter has finite amount of sea water it can filter. The Amazon page does not say anything about filter lift nor offer options to purchase replacement filters.

The device mentioned was the top hit on my google search, this question is about desalination filters in general, not this specific example in particular.

How much sea water will I be able to desalination with a portable pump before it stops working?

You can find a user manual on the website of the fabricant, and interesting comments in the product page on Amazon.
While I found no direct answer to your question, a sentence from the user manual is interesting:

During prolonged emergency use, pump the unit for at least 10 minutes each day to keep seawater from stagnating inside the unit.

So it seems that, yes, you can use it for several days in row. Also note that is is not a filter in the sense of "a device which separates solids from fluids" (wikipedia). It is based on reverse-osmosis. Actually, only 10% of the water goes for drinking, the rest is sent back to sea with a higher salt concentration. Very few salt/dirt will stay in the device.

However, this product needs:

• Yearly inspection by fabricant


• Storage and after-use maintenance (not trivial)

Also notes that the clean water production is of max 0.890 l/h. So to provide 6 people with 1.5 l a day, you'll need to pump for about 10 hours, at 40 strokes/minute. It’s not easy.

In general, for this size and type of tools, you will get similar limitations.

This is definitely a useful survival tool that might save your life. But you need money to buy it and time and discipline to maintain it. If the risk you are facing are not so big, you could consider buying something like this.

It will produce only about max 1-2 liters a day, but this might be enough to compliment the water bottles you had time to take with you while escaping your sinking boat. Also, as you're not pumping like a demon, you have more time for fishing. Moreover, it needs no maintenance, so the likelihood of it being ready for use when needed is higher.

Finally, when stranded at sea, the probability of it being the end of my life is high, drinking water or not. I would prefer to spend my last hours fishing, swimming and looking at the horizon than pumping compulsively.

You can't "filter" dissolved salt from seawater. Either the description you found is dumbed down for the masses, or just plain wrong.

It is possible to separate seawater into concentrated brine and fresh water by reverse osmosis. If managed properly, RO membranes last a long time. This is nowadays the standard way to make fresh water on ocean-going ships. The RO membranes aren't really used up or clog somehow. They can last years if the rest of the system if functioning properly.

However, that assumes that the seawater is clean by the time it gets to the RO membrane. This is usually done with ordinary filtration. Such filters do clog over time, since they trap particles. In commercial systems, there are periodic automatic backwash cycles to wash the accumulated crud from the filters.

Hand-pump RO units for emergency use don't need to work for long periods of time. Such emergencies last 10s of days at most. It seems reasonable that they could be designed so that a single fresh front-end filter can last the duration of any reasonable emergency. You then replace the filter after the emergency, and are ready for the next one.