Use of "Sure" in reply to help offering and to appreciation

In American English, "sure" is often heard in reply to offering help or expressing appreciation. I was wondering if it may not be a good choice? For example,

1. - Would you like a cup of water? - Sure.

   Is it correct that "sure" here does not have any meaning similar to thanks in advance?

   I would say "Yes, please". Even sometimes "Yes, please. Thanks!" Using "sure" makes me feel that others might think I take their help for granted.

2. - Thank you so much! - Sure.

   Is "sure" here used to emphasize that appreciation is required or highly expected?

   I would think "You are welcome" or "My pleasure" are less demanding.

In general, how shall one use "sure" in an acceptable way? What kinds of occasions can it be used, and when better not?

Solution 1:

In your first example, you could very easily replace "Sure" with "Yes "and have very similar meanings. All it's trying to convey is an affirmative response, and I would not suggest that it carries and implied Please or Thank you. Think of it as short for the following:

Would you like a cup of water? - I surely would.

In your second example, the sure is definitely not trying to imply that the appreciation is expected or required. Rather it is one of several words/phrases that have come to be commonly used in reply to thanks. E.g. no problem, certainly, etc. These all have a similar usage in practice to You're welcome.

Finally, while this usage of sure is informal, it's common enough that I'd feel comfortable using it all but the most formal scenarios, with the caveat that in situations like your first example, I'd probably make it Sure, thanks since I'm being offered something.

Solution 2:

"Sure" in the first usage is an emphatic "yes"; it implies that the second speaker is sure they will like a cup of water.

"Sure" in the second usage is a shortening of "sure thing", which in turn is a shortening of "it was a sure thing", implying that no thanks are necessary because the second speaker was certain to perform the action for which they're being thanked.