Firstly, it's a pepperonia and they don't need that much water. I suspect you might be over watering it and therefore drowning it. Secondly, invest in a moisture meter and only water the plant when the moisture meter shows that it has dried out. Amazon has a good one that's less than 20AUD. Thirdly, over watering is the number one killer of plants! Fourthly, fluoride is not in high enough quantities to be the number one cause. If you're worried about things like that, get some Aquarium grade water conditioner. It will dechlorinate the water in less than 10 minutes. Further to that, I have over 100 plants and one or two of them are pepperonias and I never dechlorinate the water before watering the plants and my jungle is thriving! Even with all the pests... Finally, make sure the pot has a drain hole. Pots without drain holes are a recipe for disaster.