Never neglect the importance of hydration during marathon training. Even if it is cold outside and you don’t feel like you sweat as much as if it were 90 degrees, you still need lots of fluid. You need to replace what you lose. You need to weigh yourself before each run and get your body weight back to that same point after a run. Do not neglect this! Even do it during pre-training runs so that you make this a habit. While running, you should consume 6-8 oz. of water every 20 minutes.
Water or sports drinks are the preferred fluids. Always drink during the two hours leading up to a run and the two hours following the run. These are your most critical times for fluid consumption. Drink water throughout the day. Sport drinks provide some advantages during the two-hour before and two-hour after windows. They provide your body with carbohydrates and electrolytes your body needs. Use both and see how you feel.
If you plan to drink sports drinks (I highly recommend Rehydrate) on marathon or half marathon day, then make sure you are drinking sports drinks on your long runs. You should not consume or drink anything on marathon or half marathon day that you have not consumed during your training runs. Hydration belts are a great way to get down some fluid while on the run. Again, consume 6-8 oz. of water every 20 minutes. This will allow you to maintain fluids while not overhydrating. Consuming too much water can lead to hyponatremia.
Some experienced marathon runners drink coffee before they run for the added caffeine. However, this is not recommended for a non-runner. Coffee in moderation (1 to 2 cups per day) is okay, but remember to drink extra water if you are a coffee drinker. Coffee and alcoholic beverages both work against your hydration. Limit both to no more than two servings per day and make sure you drink extra water. Do your best to keep your urine a light yellow to clear color. If your urine is dark, then you are not getting enough fluids and should increase your water consumption so that it becomes light yellow to clear. You must stay adequately hydrated.