How Much Water Do You Really Need To Drink?

July 29, 2019

Many sources of information say that humans need 8-12 glasses of water daily to stay hydrated and thrive. Some people take that rule literally and end up in a urologist’s office complaining of urinary urgency, frequency and leakage. Clearly, the 8-12 rule is not appropriate for everyone!

Why do humans need so much water?

Water is a vitally important part of our bodies that promotes optimal organ and cellular function. It also regulates temperature, transports nutrients and waste, provides joint lubrication, and facilitates thousands of chemical reactions that occur within our bodies.

More than half (60%) of our body weight is water. Two-thirds of which is within our cells, and one-third of which is in the blood and tissues between cells. For a 165-lb. man, that translates to 100 lb. of water weight. For a 125-lb. woman, that translates to 75 lb. of water weight.

Water intake comes from beverages AND food.

Many foods have a high water content and can be a significant source of water intake. In general, the healthier the diet (the more the fruit and veggie intake) the higher amount of dietary water. For example, melons, citrus fruit, peaches, strawberries and raspberries are about 90% water, with most fruits over 80% water. The same is true for vegetables, with lettuce, tomatoes, cucumbers, celery, radishes and zucchini comprised of about 95% of water, with most veggies over 85% water.

Our body needs water “equilibrium,” with water intake balancing water losses. Most people need a total of 65-80 ounces daily, although this can vary greatly depending upon one’s size, the ambient temperature and level of physical activity. Water losses are both “sensible,” consisting of water in the urine and stool, and “insensible,” from skin (evaporation and sweating) and lungs (moisture exhaled).

Again, water intake comes from beverages and foods consumed, with many foods containing a great deal of water (particularly fruits and vegetables, as mentioned). So the 65-80 ounces includes both beverage and food sources.

However, caffeinated beverages (such as coffee, tea, colas, energy and sports drinks and other sodas) as well as alcohol both have diuretic effects, causing you to urinate more volume than you take in. So, if you consume caffeine or alcohol, you will need additional hydration to maintain equilibrium.

How much water do I really need?

The formula that doctors use for figuring out daily fluid requirements is 1500 cc (50 ounces) for the first 20 kg (44 lb.) of weight, and an additional 200 cc (7 ounces) for each additional 10 kg (22 lb.) of weight.

So for a 125-lb. woman, the daily fluid requirement is 2250 cc (75 ounces). For a 165 lb. man, the daily requirement is 2600 cc (87 ounces). It’s important to remember that these fluid requirements include both beverages and food. If one has a very healthy diet with lots of fruits and vegetables, there will be less need for drinking water and other beverages.

The other important factors with respect to water needs are ambient temperature and activity level. If you are reading or doing other sedentary activities in a cool room, your water requirements are significantly less than someone exercising vigorously in 90-degree temperatures.

How will I know if I’m well-hydrated?

Humans are extraordinarily sophisticated and well-engineered “machines.” Your body lets you know when you are hungry, ill, tired and thirsty. Paying attention to your thirst is one of the best ways of maintaining good hydration status.

Another great method is to pay attention to your urine color. Depending on your hydration status, urine color can vary from deep amber to as clear as water. If your urine is dark amber, you need to drink more as a lighter color is ideal and indicative of satisfactory hydration.

Advantages of staying well-hydrated include:

  • Avoids dehydration and all its consequences (this is pretty obvious)
  • Dilution of urine helps prevent kidney stones
  • Dilution of urine helps prevent urinary infections
  • Helps bowel regularity
  • Maintains hydrated and supple, less wrinkled skin
  • Helps keep weight down because of the filling effect of drinking; also, thirst can be confused with hunger and some people end up eating when they should be hydrating

The only disadvantage to staying well-hydrated is that you may urinate a lot, which is not good for those with overactive bladder symptoms.

Written by Dr. Andrew Siegel

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