What are these burn marks from?

From what I’ve read online, I’m thinking that this could be from one of two things (or maybe both, who knows). My first thought is the water I’m using is too hard and causing the burn marks. I live in a major city and based on the water quality report, it looks like the water is quite hard. My second thought is maybe some sort of disease. The pot has holes on the bottom so the soil drains well. I soak the soil probably once a week and wait until it appears dry before watering again. This plant is typically inside but I try to move it outside frequently so it gets a good amount of sun.