This is cute but it would be better if it had a bigger opening at the top.
This is a nice water bottle but it needs a bigger mouth to put ice in.
ーThis is cute but it would be better if it had a bigger opening at the top.
「これ可愛いけど、もっと口が大きかったら良かったのに。」
水筒の口の部分は opening at the top のように言えます。
ーThis is a nice water bottle but it needs a bigger mouth to put ice in.
「これ素敵な水筒なんだけど、氷を入れるのにもっと大きな口がないとね〜」
「水筒」water bottle
水筒の口を mouth と表現してもオッケーです。
put ice in で「中に氷を入れる」
ご参考まで！
カナダ 
