How much water do I need to carry with me during a hike?
In warm months each hiker should carry and drink about a gallon (4 liters) of water per day. Watch your "ins and outs". Drink enough so that urine frequency, clarity, and volume are normal. You are not drinking enough water if your urine is dark, small in quantity, or non-existent in the course of a day's hiking. In addition, eating adequate amounts of food will help you replace the electrolytes (salts) that you are sweating.
During the summer months, your fluid/electrolyte loss can exceed two quarts per hour if you hike uphill in direct sunlight during the hottest part of the day. When it is so dry and hot, sweat evaporates instantly making its loss almost imperceptible. Do not wait until you start feeling thirsty to start replacing lost fluid. By the time you are thirsty, you are already dehydrated! Your body can absorb only about one quart of fluid per hour. Drink one-half to one full quart of water or sports drink each and every hour you are hiking in the heat. Carry your water bottle in your hand and drink small amounts often.