Carl Hendel, MD 1/2004
I am frequently asked how much water a person should drink. I don't know that I can really answer that question. The standard answer is eight 8 ounce glasses a day, or 64 ounces. But I have a few questions to ask about this.
Does it make sense that a 250 pound athlete, exercising on a warm, dry, sunny day should drink the same amount of water as a sedentary 100 pound 70 year old woman living in a cool, damp climate? Obviously not!
So how do we answer the question? First, if you have underlying medical problems such as kidney disease, heart disease, are taking "water pills" or other diuretic medications, have diabetes, or other endocrine problems, you must check with your doctor about your specific needs. The comments below are merely guidelines for most healthy people.
We need to replace our water losses. The average urine production is about 50 ounces a day. We also lose water in bowel movements and sweating. Also, when we have a fever, diarrhea, or vomiting, we obviously lose more water. We also get water in food and many beverages. Coffee, tea (caffeinated), and alcohol don't count, and I recommend that soft drinks ought not be counted.
So, overall, that magic number of 64 ounces does make sense, as long as we remember to tailor the amount to our personal needs and requirements.
It has often been said that you can't drink too much water. That is usually true, although I have seen a few people that did drink closer to 100 ounces a day, and they did have some abnormalities in their serum electrolytes. When they began monitoring their water intake and matching it to the suggestions above, and their intake dropped to about 60 ounces a day, the electrolyte abnormalities returned to normal. Also, there are some psychiatric conditions in which people drink very large quantities of water, and these folks do have changes in their serum electrolytes that can actually be life-threatening.
We also need to drink enough water. Kidney stones, headache, fatigue, and many other significant health problems can arise when we are chronically dehydrated.
Our bodies are very good at adapting, and usually give us good information to help us maintain healthy balance. Listening to our bodies and using common sense (as suggested above) is always helpful in staying healthy.