All of the water is polluted.

Each of the wather is polluted.
Some of the milk is bad.
Some of the apples are rotten.
All of the milk is decayed.

(Are all the expressions grammatical? - The subject verb agreement-)

1 is fine.

2 is not used.
3 is fine.
4 is fine.
5 is not used.

Your subject/verb agreement is correct for all sentences.

However, we don't use "each" with "water."

We also don't describe "milk" as "decayed." Milk goes sour or spoiled.

No, not all of the expressions are grammatically correct in terms of subject-verb agreement. Let's analyze each sentence individually:

1. "All of the water is polluted." - This sentence is grammatically correct. The subject "water" is singular, and the verb "is" agrees with it.

2. "Each of the wather is polluted." - This sentence is incorrect. The subject "wather" (assuming you meant "water") is singular, so the verb should also be singular. It should be "Each of the water is polluted."

3. "Some of the milk is bad." - This sentence is grammatically correct. The subject "milk" is singular, and the verb "is" agrees with it.

4. "Some of the apples are rotten." - This sentence is grammatically correct. The subject "apples" is plural, and the verb "are" agrees with it.

5. "All of the milk is decayed." - This sentence is grammatically correct. The subject "milk" is singular, and the verb "is" agrees with it.

To determine the subject-verb agreement, you need to identify whether the subject is singular or plural. If it is singular, the verb should also be singular, and if it is plural, the verb should also be plural. In some cases, the prepositional phrases (e.g., "of the water," "of the apples") can confuse the subject-verb agreement, so it's important to focus on the main subject of the sentence.