Not to burst the bubble or anything, but Selenium and Iodine are both elements.
The only possible way the body could "manufacture" selenium is by nuclear chemistry. As in, screwing with the electron/proton/neutron number thereby changing an element into another element.
It is impossible for the body to create elements like Selenium and Iodine. It can manufacture ionic compounds and molecules when elements are ingested because these substances are made of several elements that react with each other (whether in the body or out).
The body doesn't have the ability to create elements.
Also, Water, salt and soda are not elements. These are compounds composed of elements. Salt is mostly sodium chloride. Water is di-hydrogen monoxide etc....these are made up of elements, they are not elements themselves.