Hi Loopy.
Welcome, it's fantastic here. Really good for support if you need it.
Yes you can have sparkling water. There's even water flavourings you can buy that you can add to it too.
Good luck with this diet. If you can get your head in the right place you will soon reap the rewards.
Big YES on the sparkling water. My fave (in the quantity of it I drink!!) is the cheap on from Aldi (Moreton Hills I think). Pretty cheap, but very palatable!