Sea water with sea sand. Seawater is a complex mixture of 96.5 percent water, 2.5 percent salts, and smaller amounts of other substances, including dissolved inorganic and organic materials, particulates, and a few atmospheric gases. Seawater contains many beneficial substances like magnesium, potassium, zinc, iodine, sodium, and iron. When you take a dip into the ocean, it truly is a mineral bath for your skin. People with sensitive skin or conditions like eczema may find ocean water to be especially beneficial.