私は　小さなカップで　冷たい水を　飲んだ。 small cup 小さなカップ by or with で cold water 冷たい水 I think if you learn deeply about 「て」　「に」　「を」　「は」, you can excite to write Japanese more and more. I think "cold" means "temperature is low". Japanese "寒い" means "I feel cold". Japanese "冷たい" means "it is cold". Interesting.

I would say 私は小さい／小さなカップで冷たい水を飲みました。 I think the difference between 小さい and 小さな are subtle, but 小さい is objective whereas 小さな is subjective.

I'm not yet fluent in Japanese and still struggling and commit a lot of mistakes but I could say it like this. 私は小カップで寒い水を飲みました。 And you don't read water. ✌????️ You used the wrong verb. 読んでいます is reading. It should be 飲んでいます。

It might be something like this though I'm not so sure: 私は小さなカップから冷たい水を飲みました。