Sea water has high levels of salt and minerals, too high for human consumption.
By using the principles of water evaporation and vapor condensation, you can pull pure water vapor from sea water and condense this pure vapor as drinkable water. This technique has been used for centuries and is a primary source of drinkable water in the Middle East.
The Evaporation Step
In a clean, sealed metal pot (such as a pressure cooker) with a vent stem, heat sea water to the boiling level. Allow the first few minutes of boiling to vent into the atmosphere as this will eliminate any impurities with boiling points below that of water.
The Condensation Step
Connect a hose to the vent stem to capture and direct the steam coming from the boiling pot. The steam is pure water vapor. As the steam cools in the hose, pure water forms. Wrapping wet cloth around the hose or placing the hose in cool water will increase the efficiency of water condensation in the hose.
Place the output of the hose into a clean glass jug. The condensed water formed in the hose will be drinkable water.
Sunlight (solar heating) may be used to heat the water. Solar distillation is slow, but uses no fossil energy, making it a "green" approach.