When I paddle on salt water, if I have to spend some time on an island (weather?), it would be helpful to have a way to generate potable water from some of that salt water. Any suggestions that do not involve sunlight?

Boil and distill?
If you have fuel, could you boil water and rig up some kind of distillery?

hand powered de-salinator
I know people who have hand powered desalinators. They look a bit like oversized water filters, and can give you about a gallon of fresh water per hour.

Katadyn Survivor is one brand/model out there.

Downside is they are about $1k…

A big garbage bag
is your best friend.

The ones that do a gallon per hour are a lot more than $1k.

Garbage bag best best so far
I know what you mean. We paddle in Maine each season and usually try to camp a night or two on the island trail.

We have not found any economically and physically practical desalinator as yet - would love to - the garbage bag type alternative is your best bet until some new technology appears.

doesn’t meet requirements
Original post asked for ways not using the sun…

Here is another option that doesn’t meet the requirement (uses sun, and isn’t actually desalinating, but does reach the goal of providing water).

I’ve seen this work as part of a wilderness survival class I took a few years back.