Here is an amazingly useful open source device able to extract up to 5 liter of water a day from seawater: it's a solar water distiller. It works using the energy of the Sun, that makes evaporate the salty water and then condense it in the lower vessel.
It's called the Eliodomestico, designed by the italian researcher Gabriele Diamanti. It's available to all the developing countries through NGOs and vocational training centers.
