Unfortunately, many of us aren't getting enough to drink, especially older adults. Also, certain health conditions, medications, activity level, and ambient temperature influence total daily water intake. While the daily four-to-six cup rule is for generally healthy people, that amount differs based on how much water they take in from other beverages and food sources. But it may be surprising to learn that water intake is an individualized number. How much water should you drink a day? Most people need about four to six cups of plain water each day.