Not sure about reverse osmosis. Always go distilled to be 100% sure. A cooler of cigars is a terrible thing to mold up. As for how much to use? While you can use too little, You can't really use too much of it is a reliable fixed RH product (Heartfelt, HCM, Boveda). I try to go double the recommended amount just to make it more worry free. I would lean towards HCM or Heartfelt just for the ease of re-charging and long term cost savings.