Hola Jordi, I am not aware of any rules concerning these words. I would agree with the others that "I have much money" or "I have much water" is very unnatural and is not the way we would speak normally in day to day conversations in real life. In general, the phrase "a lot of" is much more informal and used in day to day speaking among people: "I have a lot of work to do today", "I have a lot of problems to deal with this week", I have a lot of ideas for our vacation this year." I think that you would use the word "much" or "many" in other situations. For example if you were writing a more formal paper for school or for work, or for a business presentation or for a publication: you would not use "a lot of" as this is very informal, almost slang. For example: "Do we have enough money to complete this project? No, we will need much more." (more formal than saying "a lot more money). "Do you think that we will have good results from our advertising?" "Yes, I think that many more customers will come." (better and more formal that saying "Yes, a lot of people will come." I hope that this helps and makes sense, let me know. Best of luck in your language studies!

1. I have been taught that in positive sentences I have to use "a lot of" not "much". That's OK as a general rule. It's true that we can say "I haven't got much money" or "I don't drink much coffee" but we would not say "I have much money" or "I drink much coffee". Although these sentences are theoretically correct in terms of grammar, they sound very unnatural and outdated. We might hear them in 19th-century drama, but we would not use them in modern English. Also note that we can also use 'much' in positive sentences if they're preceded by these modifying adverbs: so, as, too e.g. "I have so much money", "I have too much money" or "I have as much money as I need. 2. What's the reason for such a rule or recommendation? There is no reason: it is just the way that that the usage has evolved. 3. I heard a person who teaches English say that "much" expresses a lesser amount than "a lot of" and that's why "much" doesn't have to be used in positive sentences. Is this true? That's nonsense, I'm afraid. Unfortunately, the world is full of poorly-trained English teachers (both native and non-native) who feel obliged to invent rules. 4. Is it considered an error or wrong to use "much" in positive sentences? Yes, if you went around in an English-speaking country saying "I drink much coffee", this would not be seen as 'right'. People would understand you ( the same as if you said "He speak Spanish") , but if you asked someone to correct your English, this is one of the things which would need to be corrected. 5. In each of your pairs of sentences, the one with 'a lot of' is normal English, and the one with 'much' is not normal English. You should not use 'much' in this way. Note that this is not about formality or informality. 'Much' is equally unnatural even in formal contexts: the equivalent of 'a lot of' for more formal contexts ( e.g. academic essays or business reports) would be 'a great deal of ' or 'a large amount of' - it would not be 'much'.

I agree with the other answer. I can’t give you an explanation as it’s just one of them thing in the English language. We only use much in a negative term in your examples not positive.

Thank you, KatyLipscomb, for your contribution to this topic.

It doesn't matter whether a sentence is positive or negative. The usage of MUCH is dependent on the noun it describes. It's MUCH ado about nothing.