One way to purify water is to just boil water. This separates heat, light and gravity. By boiling water you kill 99.9% of of bacteria and vaporizes chemicals. The metal, minerals, and contamination of the pan make it more concentrated.
Ozone is a way as well. It is a very good bactericide, and has highly charged oxygen molecules to kill microorganisms. Also to kill other dissolved minerals for post-filtration and backwashing.
Another way is to use a UV light. It can be used as a disinfection and works effectively. It doesn't work as well in large bodies of water or really badly infection and chemicals.
Electronic purification and dissolved oxygen generation is another way. It creates super oxygenated water to be dissolved that lowers the surface tension of the water and effectively treats all three types of contamination, physical, chemical and biological.