One of the most common questions I am asked, both by patients and friends is how much water they should drink. I always cringe, because the answer is not what people want to hear, and that is an absolute number – half a gallon, 32 oz, 8 cups, etc.

The kidney is extremely adept in regulating our body’s water content. The concept of ‘flushing the kidneys’, while sounds appealing, does not exist. Pushing water does not protect you from kidney disease, nor does it help treat it.

How much water you need to drink on any given day depends on a multitude of factors, ranging from outside temperatures to your activity level and to your salt intake.

During hot days, if you will spend a long time out in the sun, you will need to drink more water, as you lose more through sweat; same applies if you will exercise vigorously. On the other hand, if you spend most of your time in the cool indoors, you will not need nearly as much water. Eating a meal or snacks high in salt (pretzels, salted nuts, cured meats, most fast foods) you will notice you are thirsty and you will need to drink more water until the kidney is able to excrete the extra salt.

Pushing too much water is potentially dangerous. If the kidney is not able to eliminate the excess water fast enough, a condition called hyponatremia can develop which causes symptoms ranging from nausea, vomiting to headaches, seizures and even death. Medications like some diuretics (HCTZ), some antidepressants and some chemo drugs make it more difficult for the kidney to eliminate water by itself and increase the risk of hyponatremia. Endurance athletes like marathon runners are also at higher risk due to some temporary hormonal changes that make the kidney conserve water even if not necessary; the researcher Tim Noakes, MD in his book “Waterlogged” emphasizes the risks of drinking too much water even in healthy individuals and recommends to only ‘drink as long as you are thirsty’.

There is one situation when avoiding even mild dehydration is important, and that is if you have a history of kidney stones. Maintaining a good urine flow is the cornerstone of preventing new stones from forming. An intake of 2 liters a day is recommended in that case.