'Can I have a glass of water.' Is correct. Usually it's safe to almost always use the contraction, but not in this case where a question is being asked... I wouldn't write it that way. Honestly though, in spoken English, it runs together, so it wouldn't sound too off if you said it quickly. If you said it slowly, it would sound a little strange, though.

The more correct way would be 'May I have a glass of water, please?' May makes this a request. One 'can' have a glass of water if water and a glass are available but will you be given one?

The correct sentence is "Can I have a glass of water, please?" The word "I've" is a contraction of "I have", but it's more appropriate to use the full form of the verb in this context. Using proper grammar is important when making requests, as it can show respect and politeness towards the person you are speaking to. The correct sentence is a polite and appropriate way to ask for a glass of water, and using it can help you communicate effectively in social situations. Great job!

You cannot contract the word “have” when it’s being used as the main verb of a sentence. Or in other words, when you’re using to talk about something you own: “I have a car” can’t become “I’ve a car” You can contract “have” when it’s the auxiliary verb of the sentence, usually while using the present perfect or present perfect continuous. “I have played football for 4 years” can become “I’ve played football for 4 years” That’s how it works. There is one odd exception though. In British English we often use the phrase “I have got”. EG. “I have got a car”. This just means that I own a car. We CAN say “I’ve got a car”. This is basically the only time you’ll see this contract in the simple present tense.

If you want to be polite you can ask may I please have some water. When that person gives you water then say Thank You.