Yeah, flat beer is kak.
It took me ages (sadly) to realise that a wet glass totally inhibits a head forming/lasting as well. I used to rinse my glass between different beers and wondered why the second had a rubbish head. A problem that doesn't really occur when you drink the same beer a few times in a row!
Water too? Okay, i didn't know that. I'll keep it in mind. I need to figure out what I'm doing because beer without head is not the same psychologically 😆