Where I hike the most (deserts), I often need to carry enough water to last a full day or two, so I am very conscious about the weight of water in my pack; and have been for the 40 years I have been wandering in deserts. Carrying 1-2 gallons of water (~ 4 to 8 liters) is not unusual for me, so every liter I don’t need to carry becomes even more significant.
People who have hiked with me are usually surprised with how little water I consume compared to them. This is partly due to some level of desert acclimation and of course my physiology — Â point being that all of us are different.
How much water each of us needs each day is going to be determined by our physiology, ambient temperature, humidity, hours walked, how fast we walk, elevation gain, terrain, etc.
During the night each of us is going to lose about 1 liter of water via breathing, perspiration, and urinating during the night and/or in the morning. For me, I need to drink about 1/2 liter in the morning with breakfast. Just before taking off after breakfast I usually drink another 8 ounces or so of water. Over time (50+ years of backpacking) this is what works best for me. Consuming any more water than this results in a less than optimum morning of walking.
During the day, I drink and eat when my body says I need to — that is: if feel thirsty I drink; if I crave salty foods I eat that. This is what I have learned over time. I have learned how to “listen” to my body. I only drink when I feel thirsty and I rarely drink more than once an hour. Depending on the conditions of a hike, I may not need to drink any water over the course of 10 – 12 miles, or I may need to stop once an hour and drink 1/2 liter or more at a time. Hiking 20 Km per day is a lot different than hiking 40 Km a day, which is closer to what I do on most trips (terrain dependent) and the required water and food intake can become significantly different averaging 20+ miles per day, versus 10-12 miles per day, keeping in mind the conditions of the hike. No matter what kind of hike I am doing, I am not measuring or analyzing my water consumption — I am drinking when my body says it is time to drink.
For most people, a backpacking trip is going to put more stress on their body than what they normally do each day. But if we are in reasonably good shape and not hiking in extreme conditions, we can go a couple days without food and with very, very little water — but this cannot be sustained over time. IMO, it is best to learn what our body is telling us; to learn good water management that becomes 2nd nature and will carry us through short and long trips safely.
My main concern is to keep a balance of sodium level and hydration in my body. I have found “camel-ing” up will cause me to crave salty foods quicker and I will urinate more than normal too; and I won’t feel my best after drinking too much water. This being said, day in and day out I only drink and eat what my body needs, when it needs it — no less and no more. I have become dangerously dehydrated a few times, so proper water management is very important to me because I have experienced the effects of dehydration and one doesn’t just drink a bunch of water to recuperate. I have also tried to drink too much water in the morning and have suffered ill effects. There are times when I need to drink 1 or 2 liters during the first hour or two of a hike, but I don’t drink that all at once. I want to maximize the amount of water my body needs to intake, by neither drinking too little nor too much water.
On a 2 to 3 day trip in three seasons my total pack weight is usually going to be under 20 lbs, including an “extra” liter of water that I do not drink in the morning; the “extra” 2.2 lbs of water weight is insignificant as long as I have a good pack to match the weight of everything I am carrying. With a proper pack your body won’t notice the difference between 17.8 lbs and 20 lbs. It will notice drinking too much water.
Most people are carrying a couple pounds of gear they really don’t need, and that is what I would be worrying about; not trying to save 2.2 lbs in my pack by drinking more water in the morning than my body needs.
Our packs should weigh what they weigh — we carry the gear we need for a specific trip, and we carry the food and water we need each day. There is no reason to carry extra gear, food and water that is not needed; and conversely it is crazy not to carry what we need. Listen to your body… it does not want to be over-hydrated with a liter of water, and with a proper pack and gear it doesn’t mind an extra 2.2 lbs of water — even if its brain likes a spreadsheet or scale that says it just saved a couple pounds of water weight.