Basic Water Needs

Each person has a unique metabolism and a unique need for water. There is no formula to figure out exactly how much water is required for staying healthy.  In addition, there are many variable factors that change the water needs, even for a specific person.
A person generally needs about 1/2 to 3/4 ounces of water per pound per day just comfortably existing. So, a 175 pound man needs about 3 quarts per day as a baseline.
A general estimate is that you need an extra liter of water for about every 4 or 5 miles of hiking.
This water is lost from our bodies in three main ways:

• Breathing - air picks up moisture in the lungs and we lose it when we exhale.
• Sweating - moisture escapes through the skin, even when sweating is not noticable.
• Urinating - removing waste from the body takes moisture away also.

Variables

On that baseline water need, additional water will be lost due to many physical and environmental factors, such as:

• Humidity - very low humidity allows sweat to evaporate more rapidly, cooling our bodies. This makes us feel nicer, but also increases our water needs.
• Wind - air moving away from our bodies takes moisture with it, requiring more water.
• Temperature - heat naturally makes us sweat more. The warmer the air, the more water we lose.
• Elevation - This really contributes to the temperature and humidity impact. Higher elevations tend to have lower humidity but also lower temperature.
• Exertion Level - working muscles generates heat which requires water to cool off. Limit activity levels to reduce heavy breathing and sweating to conserve water and reduce your need.
• Acclimation - a person's body becomes used to different environments over time and will learn to regulate itself more efficiently. This may reduce or increase the amount of water required for a person hiking in a new environment. Someone used to living in the desert may need less water than someone visiting there from a cooler climate.

Ways to Conserve Water

• Hike during the early morning and evening when the sun is less direct and the temperature is cooler. Rest during mid-day.
• Hike at a slow, steady pace so you are not sweating or breathing hard.
• Shade yourself with a wide-brimmed hat or umbrella.
• Know your route and where water will be available. Carry adequate water with a safety margin, but not an excessive amount. The extra weight means you work harder. Don't hike anywhere if you are not sure of available water or able to carry enough with you.
• Pick routes that have more shade, such as creeks, north sides of hills, and forested areas.