The National Institutes of Health recommends that adult males drink 13 eight-ounce glasses (about 3 liters) of liquids per day. This should be predominately made up of water, though some other beverages, such as juices, are fine. Too much coffee and tea is not recommended, as caffeine can actually have adverse effects on hydration.
If you work out for extended periods of time, your body needs more water to compensate for liquid lost through sweating, breathing and muscle use. Try adding 20 ounces (0.6 liters) of water before and during working out, drinking the water slowly rather than all at once. On very hot days and at high altitudes you should consider drinking more water as well.
The old adage recommending "8 glasses, eight times per day" will not give most men quite enough water to maintain optimum health and hydration. If you are thirsty, it means you are beginning to experience dehydration. Many men do not follow the water intake recommended, but drinking about 3 liters of water daily will help with your energy level and overall well-being.