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First of all, you need to stay hydrated, especially when it comes to running because while running, you can lose water at 18 to 35 fluid ounces in 60 minutes. This can cause dehydration so that you will be feeling sick, and even will need to go to the hospital.
So, it's obvious that staying hydrated is of paramount importance, but what's the required amount to drink before and after the run? Drink at least 3.5 fl oz of water half an hour before you start running. After the running session, regardless of its length or intensity, you need to rehydrate yourself with at least 3.5 fl oz of water. During hot seasons, humidity or long distances, you should drink twice this amount. Bear in mind that drinks like soda and juice don't properly hydrate you after a run, so it's best to drink normal water. However, after the 10k and longer distances, it's great to dehydrate with a special sports drink.
Finally, remember that it's also possible to be overly hydrated. Of course, it's not as bad as dehydration, but it can also affect your performance.