You can try a filter like the Katadyn Hiker models with carbon in. But I have filtered tannin laden water with it and it still doesn't get all the flavor out. You won't find a filter on the market that will filter down to the molecular level - so researching water sources and not taking water downstream of agriculture or industrial/mining facilities, or sulfurous hot springs, or salt water, is all you can do about things other than bacterial/cyst/protozoa that contaminate water.

About the only thing that works with tannins is to flavor it with something - like food or tea.