thirsty, you’re already on the road to dehydration.
You need to at least meet your recommended dietary allowance, or RDA, for water each day. Women need 2,700 milliliters daily, which is a little more than 90 ounces. Men need even more -- 3,700 milliliters per day, or 125 ounces, according to the Food and Nutrition Board of the Institute of Medicine. Of course, this is just the base amount of water you should drink each day; on days you run, you'll need even more.
By the time you feel thirsty, you’ve already lost as much as 2 percent of your body weight and are becoming dehydrated. Weigh yourself before going out for a run, and drink frequent small amounts of water while you’re running. When you get back in, weigh yourself again. For each pound you lose, drink 2 to 3 cups of water to keep yourself properly hydrated, suggests the American Academy of Orthopaedic Surgeons.
During the early stages of dehydration, you’ll feel tired, have a dry mouth and might also have a headache. If you don’t drink right away, your body stops producing sweat. This is especially dangerous because sweat is your system’s way of keeping your body cool. As a result, you could develop a fever and in severe cases, faint or require hospitalization.
If you’re not sure if you drank enough water on a running day, pay close attention to your urine. It should be a light yellow color -- you’ll produce more than 6 cups per day if you’re properly hydrated, according to MayoClinic.com. Dark yellow urine indicates that you’re dehydrated and you need to drink more. But if your urine is completely clear, like water, it’s a signal that you may have had too much.
Drinking Too Much
It is possible to go way overboard and drink more water than you need. When this happens, your blood becomes diluted and your electrolyte levels drop. In worst-case scenarios, this sudden imbalance impacts your heart function and your heart rhythm becomes weak and irregular. As a moderate runner though, you’re not likely to experience this condition. It’s more common for endurance athletes, such as marathon runners, who drink extremely high amounts of water.