Hallo my dear : Would it be correct to say: أنا عاوز أن أشرب ماء in fusha , you say : أنا أريد أن أشرب ماء in ammiya you say : انا عاوز أشرب ماية شكرا :)

I'm not a teacher so I can't explain grammar. But as a native, both sentences sound unnatural, especially the first one. The second sentence needs a little correction.... Bcs The whole sentence is in Egyptian dialect except for the word water, so you better say أنا عاوز أشرب ميه.

In Standard Arabic, yes, it's necessary to use أن cuz you can't use two verbs immediately togather and in this case أن + th verb will do as a noun. However, in this dialect you used, which is Egyptian, u can use two verbs, thus, there is no problem to delete أن It's more common by the way to do so. Just to learn, in the Egyptian dialect they would say, مَيَّة instead of ماء, the last one is standard.

انا عاوز اشرب ماء