Upon further inspection, Mayo Clinic is an academic medical center dedicated to research in healthcare. So they're knowledgeable in this field. In this specific article, while the original claim in the article does stick to the eight glasses of water a day, it doesn't necessarily specify it's only 8. The eight glasses of water a day is a measurement average for people to easily remember themselves. As stated, "You've probably heard the advice to drink eight glasses of water per day. that's easy to remember, and it's a reasonable goal." This acknowledges that it would be more or less a reasonable goal for people. If you'd like more accurate information, though, the same article does provide exact measurements as well for both men and women. Stating women should drink 11.5 cups and men should drink 15.5 cups of water. Other articles also, like Harvard Health Publishing, agree further with this. claiming, "For healthy individuals, the average daily water for men is about 15.5 cups and for women about 11.5 cups." Overall, both articles can agree that it all depends on what the person feels is best for them at the end of the day.
Sources: Mayo Clinic
Harvard Health