Was told that the "8 glasses of water a day" rule is a myth. it's different for each person. how much should a 5ft3, 20yr old female drink?

Doesn't matter: If you consume enough material with liquid content that you urinate at least every 6 hours you are fine. That could include applesauce (95% water),fruits and vegies (60%) or actual water. You have kidneys that help decide what to save and what to toss away and that is why you can use the simple rule.If you want to drink more, you get rid of more in the process.