You may not want to believe this and I have been ignored on this issue by the posters here, but this does work.

Sam has stomatitus. While not cured, it's not a big issue any more because I made one change. I give the critters bottled water. Nestle's is pretty good but almost any water that states that it has been purified and has minerals is good. Distilled water by the gallon also works but has no added minerals. I think the minerals give it flavor.

I do not give them tap water. The critters might think its cool, but the bacteria and chemicals in tap water irritate any current problems.

Sam was facing having major surgery after two trips to the vet inside three months. I made the change and the difference is remarkable. Someone else made that change and it worked for them too.

Good luck and I hope your kitty feels better soon whatever your decision.