The fluorine content in drinking water is very high. What should I do? My father went to work in Guizhou last month. He said that people there have spots on their teeth because of the water.

You are talking about Anshun, Guizhou, where the water quality is not high in fluorine. I live there, and I come from Guizhou. Most of the teeth with yellow and black spots I know are in rural areas of coal-producing areas, such as Zhijin and Qianxi. One is related to drinking water, the other is related to hygiene habits, and the third is tetracycline teeth (there are also such cities, but they are rare now). Don't worry, most of the water we drink now is bottled water. Some of the workers your father saw are not locals, and locals don't have this common phenomenon. If you are really worried, let him drink bottled water, and he will be fine. I don't think it's necessary to worry, but your filial piety is commendable.