theoretically water when boiled becomes distilled water, boiling water gets rid of any impurities in tap water...so you could say boiled water which is then cooled is cleaner than tap water
It's best to see a doctor for medical advice even about OTC remedies. I am not a doctor. That said, if one set of OTC remedies doesn't seem to be working it can be good to try others and, perhaps, Flonase should be something to try. Obviously, for any OTC remedy read the package to make sure that it won't cause you any danger.