Quibble about the water purifier: does it 1) just "purify" non-salt water to make it safe to drink OR 2) does it make salt water into fresh water?

If it turns salt water to fresh, it goes to number one on my list; if it is just a "purifier" of fresh water, it drops down a lot---you have to have fresh water to purify, something that may be scarce on the island. The tarp may be more useful for catching rain water.
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"Better is the enemy of good enough."