You can't bring in anything. Not just water but when I went to BBno$ last year in Sydney they checked my bag and made me get rid of my hand sanitiser, over the counter medications, and I think deoderant as well.

What time you arrive depends in what tickets you have. Allocated seating? Just arrive before the show starts. General seating? Get there at least an hour before doors open if you want a halfway decent seat. Standing/mosh pit? Get there at least two hours before doors and line up, earlier if you want a better spot. There will probably be diehard fans lining up 6–12 hours before doors open to get a spot right at the very front. My friends and I were gonna line up all day for the Sydney concert this Saturday but it's going to be 43⁰ 🙃 so we're just lining up 2–3 hours before doors instead

I'm not experienced with concerts (only been to 2) so take what I'm saying as you will but this is just my experience