Throw cold water on 「對……潑冷水」有冷卻、澆熄熱情的作用，所以這句成語是表示「掃……的興；打消……念頭」的意思。
字典上的例句:
◎ I'm sorry to throw cold water on the subject; but excuse me.
◎ Concerns about bird flu threw cold water on Ruth's plans to visit Thailand.
◎ A: When are you leaving for your business trip to Las Vegas?
B: I'm not. My boss threw cold water on the trip when he found out how much it would cost.

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我的疑問：
1.書上特別強調：注意 throw cold water on 後面是接事情或計畫，不可接人。
但是……為什麼… Dr.eye 的例句是 Don't allow them to throw cold water on you.

2."throw cold water on" 很像Chingilsh phrase, 究竟是先有 “throw cold water on” 還是先有中文的 “潑冷水” ?

哈！有趣的語言

Quote:

Language changes and very often its application expands as well.

As to whether Chinese has it first or English, it seems that English has it first. That expression was already used by William Shakespeare.

Refer to http://www.thefreelibrary.com/bs.asp?ss=text&s=throw+cold+water+on
for more details.

Tim

Just checked again and found maybe Chinese has it first. This could be just only some sort of parallel development as human minds should think alike.

In the Ming Dynasty geography book 籌海圖編, the expression 澆冷水 can be found. The original text follows:

鼓軍氣

以臣占於行陣之間，猶有未盡然者。臣視師東南，備觀怯將情狀。一聞賊戰，如澆冷水，顔色可憐。縱不便走，股已先慄，雖亦未必盡然而然者，固多矣！

Tim

Quote:

以下是網友對於throw cold water on 給予我的指導，在此提供給與我有同樣困惑的朋友參考：

Q：我的書上特別強調：注意 throw cold water on 後面是接事情或計畫，不可接人。但是……為什麼… Dr.eye 的例句是 Don't allow them to throw cold water on you.

A：因為在英文裡, 用 to throw cold water on 一個人的話, 聽起來真的就是向某人潑冷水(用桶子裡的冷水潑人!), 所以不可以用, 要不然人家要報警了^^

Q：那麼. . . . Dr.eye 的例句是 Don't allow them to throw cold water on you. 是錯的囉？

A：嗯, Dr eye 有這樣的例句嗎? 應該是不能這麼說的.. 應該改成 Don't allow them to throw cold water on your (idea/passion)等, 比較正確. 或是說改成 Don't let them stop you 也可以.

Q：“....that they are sometimes obliged to throw cold water on him....” Oh, it still confused me!
Refer to http://www.thefreelibrary.com/bs.asp?ss=text&s=throw+cold+water+on

A：不用太困惑啊.. 這裡的...that they are sometimes obliged to throw cold water on him.... 的確就是實質上用冷水澆上那頭熊的.. 因此直接用 throw cold water on him 並沒有錯. http://irving.thefreelibrary.com/Adventures-of-Captain-Bonneville-USA-in-the-Rocky-Mountains-and-/1-39#throw+cold+water+on[/color]
The bears are soon attracted by the bait. ... draw him in triumph to the scene of action. By this time, he is exasperated to such frenzy, that they are sometimes obliged to throw cold water on him, to moderate his fury. 也就是說, 把冷水潑上熊以控制它的情緒, 要不然萬一熊脫綁的話旁邊的人就完了.

再為您總結一下好了.. 當諺語「對……潑冷水」用做「掃……的興；打消……念頭」的意思的時候, 不能接人. 如果接人或動物的話, 就不是諺語了, 而是真正潑水的動作.

Quote:

找碴？這是誰家的孩子？打破砂鍋璺到底，還問砂鍋在那裡？

曾借用您的問題求教於其他人士，所獲得的結果大致如下：
http://www.winnerenglish.com/web/BBS?command=detail&postId=102180&groupId=8710&FP=17609

Dr.eye 的例句 Don't allow them to throw cold water on you. 如果不看其中文翻譯「別讓他們打擊你的士氣。」，加上沒有上下文可以參照，或可解釋為字面上潑水的動作，如不作諺語用，則無錯誤可言。

我曾致函Dr.eye客服中心，希望能獲得令人滿意、令我意外的解釋，迄今一個月過去了仍未獲任何回應。今天如果沒有您的提醒，自己還真忘了有這件事。

能在不疑處有疑、追根究柢、鍥而不捨，這般的問學精神值得我向您學習，也感謝您的分享。