A mug

You’re wrong. No one will argue over a cup of water.

Just because it looks clear doesn't mean it's not polluted with contaminants.

That's 3/4 of a cup of water.. it isn't filled to the rim.

A cup is a defined volume. Without graduations, there's no way to know if that's a cup of water or not.

It’s a glass of water!

That's vodka and you know it.

U mean a glass?