水を一杯

a glass of water

→ 水
phrase Rare #32,372
a glass of water 一杯 means “one cup/glass” here and is used as a counter for drinks. 水を一杯ください is a polite way to ask for a glass of water.
JA: レストランで水を一杯お願いします。
EN: A glass of water, please.

水を一杯下さい

A glass of water, please.

ビルは私に水を一杯持ってきてくれた

Bill brought me a glass of water.

水を一杯いただけますか

Could I have a glass of water, please?

水を一杯持ってきてください

Please bring me a glass of water.

水を一杯いただきたいのですが

I’d like a glass of water, please.