I would try talking to your mum again but before you do think carefully about what you want to say and write it down and all the things you have just talked about, tell your mum you need to have a serious talk with her and arrange a time to sit down with her and refer to what you have written down and any answers to questions she might ask, I know this sounds like alot but you need to show her your serious and concerned about a number of things happening in your home , she sounds like she's trying to keep you safe but I think there's more going on, I really think you need to use your phone and find someone near you that you can talk to like an authority figure such as a counselor or psychologist, even a phone appointment if you can't go in person just tell them you really need some help and advice and support, someone who is independent, or call your school and tell them you need to speak to a counselor urgently they can't turn you away, Covid can't be used as an excuse to keep you isolated, I think you have legitimate concerns but start with your mum and then go from there if you feel she's not listening, and tap water where you are would be perfectly fine to drink as much as you want, most people don't buy bottled water