as weak as water 弱不禁风；身体虚弱

【例句】
He's as weak as water when it comes to saying no to a friend.
当需要谢绝一个朋友时，他显得非常软弱无力。

Sir, I am only just getting well of a fever, and I am as weak as water.
先生，我刚刚退烧，现在我身体虚弱。