First Time Faster

Hey so I am thinking about doing a water only fast in the next couple weeks(once my food runs out) and I was wondering if someone could answer a couple questions I have. I have done a fair bit of research but I have never actually done a water only fast. The first question I have is, how will this affect my weight. I am 21 years old, 5'7, a guy, and I weigh just over 140 pounds. Now, the only concern I have is that I do not have a ton of fat on me. I do have some, but I was wondering at what point will I go from burning fat to burning muscle? I was thinking I would fast anywhere from 10-20 days. Other questions I have are if the type of water I drink matters. I drink bottled water from the store, Nestle purelife ones. They just come in 32 packs of plastic bottle. It anyone has any knowledge on that it would be appreciated. The last question I have is what effect herbal tea will have on the fast. I was told once that a little honey and herbal tea have little to no effect on fast results. Is this true? I was thinking cocao/cinnamon/chili tea. Any input is appreciated.