If you are in fact boiling the grains, or soaking them in ro water and taking them out just prior to hitting boiling temps, the pH is likely high enough to extract harsh tannins from the husks. You do want to remove the grains so that this doesn't happen.
A second thing that sometimes happens when folks top up with tap water is that they don't remove the chlorine before adding it to the beer. This will usually cause a chlorophenolic flavor/aroma to form, which is usually perceived as chloraseptic, band-aids, cloves or plastic. RO will help to eliminate that, if that has been contributing to the perception of these flavors.
HTH-