The amount of water a person needs to drink in a day can vary based on factors such as age, sex, weight, activity level, and overall health. However, a general guideline recommended by health authorities is the "8x8 rule," which suggests drinking eight 8-ounce glasses of water a day, totaling about 64 ounces or roughly 1.9 liters.

In recent years, more personalized recommendations have emerged, taking into account individual factors. The National Academies of Sciences, Engineering, and Medicine in the United States suggests a daily water intake, including all beverages and food sources, known as the "Total Water Intake." For most adults, they recommend about 3.7 liters (125 ounces) for men and 2.7 liters (91 ounces) for women per day. This includes all fluids consumed, not just water, and moisture content in food.

It's important to note that individual water needs can vary, and factors such as climate, physical activity, and health conditions can influence hydration requirements. Thirst is a good indicator of when to drink water, and urine color can be a helpful gauge of hydration status – pale yellow to light straw is generally considered a sign of adequate hydration.

For personalized advice on water intake, it's advisable to consult with a healthcare professional or a registered dietitian who can take into account individual health factors and lifestyle.