There is no question that water is vital to the body's overall health. We use water for transporting nutrients and wastes, lubrication, temperature regulation, and tissue structure maintenance. In addition, plentiful fluid consumption may be protective against diverse medical conditions, including kidney stones, constipation, colorectal cancer, premalignant adenomatous polyps and bladder cancer. Water deprivation results in life-threatening dehydration within a few days. Loss of body water exceeding five percent of body weight leads to decreased endurance, culminating in heat exhaustion.
With that being said, how much water do we really need depends upon several factors such as:-
On average, women who are adequately hydrated consume about 2.7 liters (91 fluid ounces) of total water a day. Since food typically accounts for about 20 percent of fluid intake, this means drinking roughly 2.2 liters (74 ounces or about 9 cups) of beverages a day.
While drinking water is often the best way to replace lost fluids, other liquids including milk, tea, soup, fruit juice and sports drinks also are effective. For a healthy adult, fluid intake is probably adequate when one rarely experiences thirst and when urine is colorless or slightly yellow. As adults get older, they may experience less thirst, so it’s advised to drink before thirst sets in. Signs of inadequate fluid intake may include dry mouth, headache, light-headedness, little or no urination, and constipation.
My best answer... As much as you think you need to drink in a day, drink more. I don't judge it on how much I take in as much as I judge it on how much I am expelling. If I am out working and I am sweating and hydrating and not going to the bathroom, I know that I need to be drinking more. If my urine is not as close to clear as possible, I know that I need to be drinking more water. I am horrible at drinking enough water, but my wife has been doing a really good job keeping me on track lately. I am not going to give you an amount in ounces or liters or anything like that. I will just reiterate, when you think you have had enough water to meet your daily quota, drink some more.
The answer to this question varies from person to person and from situation to situation. If you want to standardize an answer, it would be the volume of water necessary to keep a serum sodium concentration of about 140 mEq/L. During the summer, exercise or while having fever, the insensible losses of water (evaporation through the skin and breathing out water vapor) are higher than normal, so more water is needed for replacement. People who form kidney stones, need to drink more water to dilute the urine and to reduce the stone formation. On the contrary, people who have heart failure, or increased ADH in their system product of cancer, infection or dehydration have kidneys which retain water and drinking too much water can lead to water intoxication or hyponatremia (low sodium concentration). To summarize, the answer is: IT DEPENDS...