The famous eight-glasses-a-day rule has no solid scientific origin. U.S. adequate-intake estimates land around 2.7 liters a day of total water for women and 3.7 for men — but that's TOTAL water, counting every beverage plus the roughly 20% that comes from food. Fruits, vegetables, soups, and yogurt are quietly hydrating you all day.
For most healthy people, thirst is a genuinely good guide, and urine color is the easy check: pale yellow means you're fine. You'll need more in heat, during exercise, when you're sick, or when pregnant or breastfeeding. And yes, you can overdo it — drinking extreme amounts in a short time can dangerously dilute your sodium (it's rare, mostly seen in endurance events). Hydration is worth caring about; it just doesn't require an emotional-support gallon jug.