The inhabitants of these islands rely on the water they get from their food – primarily coconuts. But they have loads of sun shine.
We use this to drive solar pumps. So during the day, they pump sea water up conical structures – as when sea water is under a meter high, the water boils.
Losing all contaminants and salts. We then have a chain of vacuum pumps, to transport the water into the interior – where we erect water reservoirs.
When we vent the water vapour, we get cold water. That will fill the tank. We then have pipe lines, distributing the water to the villages. So for the cost of the vacuum pumps and pipes lines, we get fresh water.
Charities like Water Aid should build the infrastructure. This works all around the world – covering sea or river water into fresh, drinkable water.