A teenage girl should drink about 7 to 11 cups of water per day, depending on her age. Girls aged 9 to 13 need roughly 7 to 8 cups, while those 14 to 18 need 8 to 11 cups. These numbers cover plain water and other beverages but not the water that comes from food, which adds another 2 to 4 cups on its own.
Daily Water Needs by Age
The simplest guideline breaks down by age group. Girls between 9 and 13 should aim for 7 to 8 cups of water a day. Once a girl turns 14, that target rises to 8 to 11 cups a day, reflecting a larger body and higher metabolic demands. A cup here means 8 ounces, so 11 cups works out to 88 ounces.
There’s also a quick formula that works well for younger teens: take half your body weight in pounds, and that’s roughly how many ounces of water you need daily (this rule of thumb applies up to about 100 pounds). A 90-pound 13-year-old, for example, would aim for about 45 ounces, or just under 6 cups. For older or heavier teens, the 8-to-11-cup range is more reliable.
These recommendations refer to beverages you drink, not your total water intake from all sources. About a third of the water your body uses each day actually comes from food, especially fruits, vegetables, soups, and yogurt. So even if you’re not hitting 11 cups from your water bottle alone, the moisture in what you eat closes some of that gap.
How Exercise Changes the Numbers
Physical activity increases water needs significantly. Teens aged 13 to 18 should drink 11 to 16 ounces for every 20 minutes of active sports or intense exercise, according to Johns Hopkins Medicine. That’s noticeably more than the 6 to 12 ounces recommended for adults in the same timeframe, because adolescents generate more heat relative to their body size and are less efficient at cooling down through sweating.
If you’re at a two-hour soccer practice, for instance, that could mean an additional 66 to 96 ounces on top of your baseline intake. Drinking water before, during, and after activity matters more than trying to catch up afterward. Starting practice already dehydrated makes it much harder for your body to regulate temperature.
Does Your Period Affect How Much You Need?
During the second half of the menstrual cycle (the luteal phase, roughly the two weeks before your period), your resting body temperature rises slightly. This happens because of shifts in progesterone, which pushes your internal thermostat up by about half a degree Celsius. That might sound like it would make you sweat more or need extra water, but research from the Gatorade Sports Science Institute shows that overall sweat rate stays the same across the entire cycle.
Estrogen does lower the threshold for feeling thirsty during this phase, so you may naturally reach for water more often. But studies tracking actual fluid intake during exercise found no meaningful difference between cycle phases. The practical takeaway: you don’t need to calculate different water targets based on where you are in your cycle. Drinking when you’re thirsty and following the general guidelines covers it.
How to Tell if You’re Drinking Enough
Urine color is the fastest check. When you’re well-hydrated, your urine should be a pale, straw-like yellow. The more water you drink, the clearer it becomes. Darker yellow or amber urine means you need more fluids. If your urine looks orange, that’s a stronger signal of dehydration.
Other signs you’re falling short include headaches (especially in the afternoon), feeling unusually tired, dry lips, and difficulty concentrating at school. Many teens mistake mild dehydration for hunger, so if you’re snacking constantly but still feel off, try a glass of water first.
Can You Drink Too Much?
It’s rare, but possible. A condition called water toxicity happens when someone drinks a very large amount of water in a short period, faster than the kidneys can process it. This dilutes sodium in the blood to dangerous levels. There’s no official upper limit for daily water intake because healthy kidneys handle extra fluid well under normal circumstances. The risk comes from extreme situations, like chugging several liters during a dare or drinking excessively during a long athletic event without also replacing electrolytes.
For everyday life, spreading your water intake across the full day is both safer and more effective than trying to drink it all at once. Keeping a reusable bottle with you and sipping throughout the day is the easiest way to stay on track without overthinking it.
What Counts Toward Your Daily Intake
Plain water is the best option, but it’s not the only thing that counts. Milk, herbal tea, flavored water, and even juice contribute to your daily fluid total. Caffeinated drinks like iced tea do count, though caffeine has a mild diuretic effect that offsets some of the hydration benefit.
Foods with high water content make a real contribution too. Watermelon, cucumbers, oranges, strawberries, and lettuce are all above 90% water by weight. Soups, smoothies, and yogurt also add up. Research on children and adolescents in the UK found that food moisture accounted for about 33% of total daily water intake, with beverages covering the remaining 67%. So a teen who eats plenty of fruits and vegetables is already getting a meaningful portion of her water needs met before she takes a sip from her bottle.