The old adage of not needing to drink unless you're thirsty does still holds true when you're walking as it's extremely important for your body that you keep it replenished with fluids. When you're walking, you're sweating and, therefore, getting rid of a lot of the fluids in your body. It's important for your health that you refill your body with fluids. This will also make it easier for you to continue walking comfortably.
The kind of fluids that you should drink when walking will have a lot to do with the kind of walking as well as the duration. Sports drinks are recommended if you're planning on walking for 30 minutes or more, such as a marathon or walkathon. Sports drinks have electrolytes and carbohydrates that will not only provide your body with energy buy will also help your body to absorb water quicker.
Some walkers try to dilute the sports drinks or eliminate them altogether to avoid consuming the calories. Diluting them will only decrease the benefits of the drink. It's important for your body that you drink sports drinks that have carbohydrates. You may choose a drink that's low calorie but will still replace the salt you're losing when you walk. Many specialists recommend that you drink whatever beverage you enjoy the most as long as you're drinking something. Many bikers prefer just plain cold water. The best way to determine if you should drink is if you're thirsty as your body will not lie to you.
It can be just as dangerous to drink too much as it can be to drink not enough. If you don't drink enough you can become dehydrated while you can get hyponatremia (low blood salt level and fluid overload) if you drink too much. Weigh yourself both before and after you begin walking. A rule of thumb is that you should not have a weight loss or gain of more than 2%. If you do, it's an indication that you've been drinking either too much or too little.
A good rule of thumb for walkers is 1 cup of water for every mile walked. Your weight will also determine the amount. If you weight pounds, you'll need a half cup while a 200 pound person will need a full cup. Obviously, the slower you walk, the less you'll need because you won't be losing it as fast. All things said, let your body do a lot of the deciding for you.