I read your writing well.

But there is something I want to refute in your writing. 

You told the example like this ; "if you will go to a library and drink the water of 1L frequently in disposable cups, you would use five little disposable cups which could put water about 180ml. However, tumblers can be reused several times. If you go to a library for five days and use disposable cups, you will waste 35 disposable cups, which would occur a lot of bad environmental pollution." right?

However,  you don't know the fact that people use paper cup (disposable cup) many times, over and over again. So I quote that you said and restate,  if people go to a library and drink the water, they don't use 35 disposable cups but 5~6 disposable cups.

Finally, I heard on the basis that tumblers can be reused several times. That's probably the reason that people use tumblers and the biggest advantage of using a tumbler. But I think it's useless because people don't use it for a long time. Tumbler needs to be washed after use it, so people use it once when they to be outside. But you don't have to wash paper cups. You just use it several times and throw it away. This would be convenient than a tumbler.