Picture the person at the edge of the field with an armful of bottles. He arrives before the players and leaves after them. When the whistle goes he runs on, hands out water, and runs off again. He wears the team's colours and the job really needs doing — but no point, no win and no headline will ever have his name on it. Both uses of water boy come out of that position: on the team, next to the action, and not part of it.
可以想成球場邊那個抱著一堆水瓶的人。他比球員早到，比球員晚走。哨聲一響就跑進場遞水，然後又跑出來。他穿著球隊的衣服，這份工作也真的得有人做，但得分、勝利、新聞標題都不會寫上他的名字。water boy 的兩個意思都從這個位置長出來：在隊裡、在旁邊、不在場上。
From the word’s history
Wiktionary gives the origin plainly as water + boy: the boy who brings the water. The compound still says exactly what the job is.
Wiktionary 記的來源很單純：water（水）+ boy（男孩），就是「拿水的那個男孩」。這個字到今天還是照字面在描述那份工作，所以即使做的人是成年人，名稱也沒有換。
Wiktionary, "water boy"
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