So, to answer the big question: a glass of water is 8 ounces. It’s a neat, round, human-friendly number. It’s the amount that makes the “eight glasses a day” advice actually work without needing a calculator.
Now, go pour yourself a glass. Maybe it’s 8 ounces, maybe it’s 10. Who’s measuring, really? The point is, you picked up the glass. And that, my friend, is a win. Your body just did a little happy dance, even if you didn’t feel it. Cheers to you, and to keeping things simple.