Making sea water into drinking water requires removal of the dissolved salt that, according to the U.S. Geological Survey, makes up approximately 35,000 parts per million (ppm) of sea water's chemical composition. Removing the salt from sea water, or desalination, on a large scale is extremely expensive, but creating enough pure water from sea water for personal use is surprisingly cheap and easy, and turns on the sun's power to evaporate and purify water.
Find a small piece of land that gets full sun exposure and dig and use a shovel to dig a hole approximately two feet deep by three feet across.
Line the hole with a plastic tarp.
Place a heavy cup or bowl at the bottom center bottom of the hole and fill the hole around the cup/bowl with sea water, making sure the sea water does not rise higher than the top of the cup/bowl.
Cover the hole with a plastic tarp and secure it to the ground around the hole with rocks, then place a small rock in the center of the tarp directly over the cup/bowl.
Wait for the sun to evaporate the sea water. The sun evaporates the sea water, and fresh water creates condensate on the underside of the top tarp, which runs along the plastic down to where the small rock creates a dip over the cup/bowl. The fresh, condensed water drips into the cup/bowl at the top tarp's lowest point, i.e., at the point where the small rock makes the tarp dip toward the collection cup/bowl.
After several hours remove the top tarp, then remove the collection cup/bowl from the center of the hole along with the fresh drinking water inside.