A while back I wrote a post about the Nathan Speed 4 Water Holder. I thought this nifty gadget was great for long-distance runners, since it holds a total of 40 ounces of water. After reading the post, a user had a great comment.

How much/often should you drink while running?
— bicyclebeth

I'm sure many of you are wondering the same thing. To find out what I think, read more.

Staying hydrated is a necessity, so here are some rules I like to follow:

• An hour or two before a long workout, drink 16 ounces of water or a sports drink like Gatorade. This will help prevent dehydration and also keep you feeling alert.
• During your run, sip eight ounces of fluid every 20 minutes. Plain water is fine if you're running an hour or less. If your run is longer, you'll need to replenish lost electrolytes, so Smartwater or a sports drink are better options. You can also use a combination of Gu or Luna Sport Moons with water.
• Hydrate proactively. Don't wait until you feel thirsty to start drinking, since this is an early sign of dehydration.
• Avoid drinking too much water, because it can lead to a potentially fatal condition known as hyponatremia, or water intoxication. This is when you have dangerously low amounts of sodium in your body. It usually happens on long or hot workouts, if you lose a lot of sodium through sweating and consume a ton of plain water. This sets off an electrolyte imbalance, so opt for sports drinks instead.
• Lastly, after a run that's an hour or longer, rehydrate with 16 to 24 ounces of sports drink for every pound of water weight you lost during your workout.

Source