No, it is incorrect. The adjective 'many' is a word for a large and indefinite number. The noun 'water' is an uncountable (mass) noun. An uncountable noun can't be described by number, even an indefinite number. An uncountable noun can be described by amount, such as some, a little, a lot, a great deal, etc. The closest adjective to 'many' in terms of amount is 'much'. The correct term would be 'much water'.
A water operator is grammatically correct.
Yes, the sentence is correct grammatically. The sentence is The frogs were in the water.
no
It can be, like in the following sentence. There were many firsts in this historic week.
"Not like that" can be grammatically correct, depending on the context.
Yes! That is grammatically correct!
Yes, 'for free', is grammatically correct.
"How many beans?" is grammatically correct.
This is not grammatically correct. The correct form is 'you do not know', or the abbreviated 'you don't know'.
Sure. It would also be grammatically correct to write He spoggled his nubbix on the goober. Grammatically correct and meaningful are not the same.
"That was wrong" is a grammatically correct sentence.
'What a drunkard you are' is a grammatically correct English sentence.