“Make” isn’t quite the right word. DIY salt is really EIY salt. Evaporate It Yourself.
When the water is gone from seawater, what’s left is sea salt, and more than you might think: A four-gallon bucket of water will yield more than a pound of salt. The following steps work best if you have a wood stove or a radiator; it doesn’t make financial sense to use the stove top. You also can evaporate the seawater in the sun in a shallow pan, which takes considerably longer, depends on how much sun you get and requires many consecutive dry days.
1. Get seawater. Strain it through a coffee filter to remove big impurities. Don’t worry about microorganisms; nothing survives in salt.
2. Let the water evaporate. If you use a wood stove for heat, you can humidify your house and manufacture salt in one fell swoop. Heat the water in an enameled cast-iron baking dish or casserole (9 by 13 inches is good; you need a wide expanse of surface area). The process will take a couple of days or up to a week, depending on how much heat you use.
3. Harvest. Once the salt begins to form, stir every once in a while to break up clumps, but don’t worry about being too vigilant because you can grind it later. The salt is done when it’s dry to the touch. The consistency will be a little clumpy and moist-looking. Store in an airtight container; if you leave this DIY sea salt exposed to the air, it will return to a soupy, slushy state.