"Three beers, please" is more common than "Could we have three glasses of beer, please." In the same way it's common to say "Two sugars, please," when asked how much sugar you want in your coffee. Sugar is uncountable, but teaspoons are. The question is "How many teaspoons of sugar do you want?" However, it's much easier to shorten it to "How many sugars?" The quickest answer is "Two." The next quickest is, "Two sugars." The longest is, "I'll have two teaspoonfuls of sugar, please." This is very polite, but a lot of words. For paper we'd probably say, "Two sheets, please" (not two papers) It's neither 'correct' nor 'incorrect' to shorten "Three glasses of beer" to "Three beers." It's a matter of situation and style. I normally use shortened versions...as long as I'm going to be understood. If there could be confusion, I use the full version. So, beers all round! (A glass of beer for everyone!) Cheers!

Yeah, you could say ''two waters" and it will be understood by whomever is selling it or handing it to you. For instance at the theater, I always hear people saying "Can I have a (bottle of) water please". In a case where it might be ambiguous to say just 'water', then you would have to specify: gallon, cup, glass, bottle, etc. As for paper, you could say ''a piece of paper'' or a ''sheet of paper''. "Papers" is often understood as an ''essay'', specially in a school environment. ex: I have two papers due tomorrow and I haven't started yet! Please hand in your papers before the end of class. :)

Yes, all of these examples are correct, but the issue here is not whether it's conversational English or not. It's about the underlying sense of the word in a particular context - either informal or formal, written or spoken. As you no doubt learnt in your elementary grammar class, words such as 'water' and 'coffee' - when they refers in general terms to the liquid or solid substance - are grammatically uncountable. That is to say they takes singular verb, are modified with 'much' and 'little' and 'some', can't take the indefinite article 'a', and have no plural form. However in many situations, when we use the word 'coffee', for example, we don't mean the substance in general terms. eg Do you want a coffee? Can we have two coffees, please? Here 'coffee' is a 'shorthand' form for 'cup or cups of coffee' ie countable. or They sell all sorts of different coffees in that store In this example, 'coffees' is used to mean 'varieties of coffee'. So, in other words, you have to think of the 'real' meaning of the word in each specific context, and ask yourself if you are speaking in general terms (about a liquid, a powder or whatever) or in specific terms about something which can be counted (such as cup or variety). I hope that's clear. I'll answer your specific questions in another post soon!

About the specific questions in your query. The reason that people don't say 'Four glasses of beer' very often is nothing to do with the grammar of the sentence. In fact, with beer, you would normally also specify the type or brand, rather than just 'beer'. But to get back to the question of quantity, the fact that we don't say 'Four glasses of beer' is more to do with the fact that it's not very informative or helpful. You'd say ' A pint of beer/ two pints of beer/ a half-litre of beer/ three halves of beer . On or in other words, you'd say what size of glass you want. The same with 'bottle' - if it's a drink that is usual served in a bottle then you don't need to say it. It's the same with 'coffee'. Coffee is usually served in a cup, so you don't need to say it. You'd say 'two black coffees' 'two large coffees' etc. Regarding the question of paper, yes, you are right that the 'substance' paper is uncountable, but often we use that word with a slightly different meaning . 'Two papers' doesn't mean 'two sheets/pieces of paper' . As Sandrah suggests, if you hear 'two papers' it's probably in an academic context, and it means something like a thesis or dissertation. It is also used countably for parts of an exam. Some examples. eg 1. Paper was invented in China thousands of years ago. 2. When you go to the shopping, can you get me some paper? 3. When you go to the shopping, can you get me a paper? 4. Which paper do you prefer - the plain or the patterned one? 5. The exam is divided into three papers - reading, writing and listening. As you can see in 1 and 2 , 'paper' is uncountable - this refers to the substance. In 3, the listener would understand 'a newspaper' = countable. In 4, you are talking about 'types of paper' = countable. In 4, the word 'paper' refers to parts of an exam = countable. I hope all that answers your questions!

Thank you so much, everyone! Your all explanations are really helpful. I guess they are not explained in general textbooks. "Two waters", it's very easy to say and sometimes bottles or something are specified depending on situations: They all make sense to me. Also, I can understand the difference of the use of "paper" such as "a (news)paper", "a piece(sheet) of paper" I appreciate that.