Yes, it is safe to drink the water in Belize, but I choose not to drink it personally. Bottled water tastes better for me. I have a filter at my house, so I drink filtered water.
There is a guy from Canada I know, who woke up at midnight and was thirsty. He didn’t have any bottled water in his room, so he just went for the tap water. We spent a few days together and he had no issues. But he had already been to Panama and Costa Rica, and he had trouble with the water there.
We have noticed that when people move from North America to Belize or Central America, they are not used to the water because our water is different. Our tap water is not purified water; it’s treated water. It is filtered and has chlorine in it. Locals have no issue with it, but for people who are new to our water, they may have an upset stomach after drinking it, perhaps causing diarrhea for a couple of days. But they get treatment and then they’re okay.
Some expats do not even drink the water, but get an upset stomach from the ice that was not made with purified water or from brushing their teeth with tap water. It gets to them at first, but after living here for a couple of weeks, they get immune to the water, and it is no longer unsafe for them to drink the water in Belize.