I drink the Propel zero sugar electrolyte water, and drink about 4 a day (so 67.6 oz total)
I also have this cup with colorful bands that you can move up and down for how many bottles you drink per day. This is the same exact bottle I have! I struggle with drinking enough because of my gastroparesis and plain water making my stomach hurt and causing nausea (no fucken clue why but it does...) so I just call it good.
If you have POTS, I’m sure you know that you need a fuckton of salt, and some people swear by the SaltStick things. These are the brand I have but they hurt my stomach like a bitch.
I hope this was helpful, and I hope you find some results soon :)