The glass surface is smooth and easy to clean, especially bacteria and dirt are not easy to breed on the glass wall, so drinking water from the glass is very healthy and safe.
Ceramic cups have similar characteristics to glass, but many ceramic cups are easy to add harmful glaze during firing, which easily leads to excessive lead content. Therefore, in the selection process, glass is the best, followed by ceramic cups. Unglazed pure ceramic cups are as safe as glass, and unglazed ceramic cups are like white bowls for eating.
Enamel cups are also safe, but if you drink tea, it is easy to get dirty and difficult to clean.
The above three kinds are the safest, followed by stainless steel, but they are also oxidized and discolored.
The most unsafe things are paper cups and plastic cups. It's okay to use it once or twice occasionally, but don't use it every day.