Okay. You just washed up on a small island with no apparent source of fresh water and all you have is a PSK or your EDC plus PSK. You can build shelter from plants. You can fish or trap sea creatures for food. You might get lucky and have a few cocunut trees or various edibles.

With the exception of rain and dew collection what do you do for fresh drinking water?

You might have one trash bag to build a solar still. You would have to construct away from the tide. You would have to haul plenty of water to keep it going. Would this be enough to keep you alive?

You might get lucky and have some kind of foilage to put a transpiration bag on.

In the long run you might be stuck on that tiny island for a long time. Remember "Cast Away" The only drinking water Tom Hanks had was rain water he collected.