1. We can't say 'How's right'? The question word 'How..?' cannot be the subject of a sentence. Your question should be, for example, "Which is right?" , "Which one is right?" or "Which one of these sentences is right?" 2. The correct option is "Let's fill your bath with warm water". This is because 'water' is an uncountable ( or 'mass' ) noun. Water is 'stuff' - a substance, not a thing. This is why we don't use an 'a' before it. Similar sentences would be 'Fill your cup with hot coffee' or 'Fill your plate with tasty food'. As you can see from these examples, we don't use the indefinite article with uncountable nouns. I hope that makes sense.

The first one ! water is non_count noun . and we don't use a or an before non -count nouns.

Hi Natalya, the answer is "let's fill your bath with warm water" The reason is that there is a difference between certain types of nouns. Water is a noun that cannot be divided, you cannot have A water. You can have a bucket of water or a drop of water but you cannot have A water. Also your question should be "Which is right?" not "How is right?" Helen

It's "warm water" not "a warm water". So "Let's fill your bath with warm water" is better. However I wouldn't naturally refer to filling the bathtub if I was talking about bathing/cleaning. I might say "let me make you a warm bath" or "let's get a warm bath ready for you". Michelle https://www.italki.com/michelle

Вода - неисчисляемое существительное. Для таких существительных неопределенный артикль "a" не используется. Его можно использовать, если количество воды известно, например - a cup of water.