What is the meaning of come hell or high water ?

"Come hell or high water" makes clear that some future event will happen and no other event will stop it from happening. Example: "Will you be at the family reunion next year?" Answer: "Yes- we'll be there, come hell or high water!" Even if events became totally chaotic ("hell") or there were natural disasters ("high waters") the future event would still occur.
*The word "hell" is informal and should not be used in polite situations.
「不管怎樣」講清楚某一未來事件將發生，並且其他事件從發生不會停止它。 例子： 「您明年將是在家庭聚會？」 答復： 「是我們將在那裡，不管怎樣!」 即使事件變得完全混亂(「地獄」)或有自然災害(「水位高」)未來事件更將發生。 *The詞「地獄」是不拘形式的，並且不應該用於禮貌的情況。

come hell：去地獄，因為[hell]代表地獄
feel like a fish out of water：因為魚出水會死，所以[feel like a fish out of water]代表很難受，就快死等意思