I recently watched a video of a man who was going to be hiking and camping for several days, out and back, on a trail that had no water access. That meant he and his friends had to carry their entire excursion’s water in their packs, for food prep (backpacking meals), and hydration. One guy on the trip elected just just chuck a bunch of commercial water bottles into his pack. That got me thinking, how much weight is added for every commercial water bottle added to a hiker’s pack?
And of course that mostly depends on how much volume a particular water bottle has, the actual weight of the bottle itself being negligible, so I thought I’d make a helpful reference table that shows weight as a function of number of bottles and the size of those bottles, so hikers need not fumble around with their calculators when planning a trip:
Added Weight of Packed Water for Each Bottle Packed (Pounds)
| Size of Water Bottle | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| 12 oz (355mL) | 0.78 (lbs) | 1.56 | 2.34 | 3.12 | 3.91 | 4.69 | 5.47 | 6.25 | 7.03 | 7.81 |
| 16 oz (473mL) | 1.04 | 2.08 | 3.12 | 4.16 | 5.20 | 6.24 | 7.28 | 8.32 | 9.37 | 10.41 |
| 16.9 oz (500mL) | 1.10 | 2.20 | 3.30 | 4.40 | 5.50 | 6.60 | 7.70 | 8.80 | 9.90 | 11.00 |
| 20 oz (591mL) | 1.30 | 2.60 | 3.90 | 5.20 | 6.50 | 7.80 | 9.10 | 10.40 | 11.70 | 13.00 |
| 24 oz (709mL) | 1.56 | 3.12 | 4.68 | 6.24 | 7.80 | 9.36 | 10.92 | 12.48 | 14.04 | 15.60 |
| 1L (33.8 oz) | 2.20 | 4.40 | 6.60 | 8.80 | 11.00 | 13.20 | 15.40 | 17.60 | 19.80 | 22.00 |
| 1.5L (50.7 oz) | 3.30 | 6.60 | 9.90 | 13.20 | 16.50 | 19.80 | 23.10 | 26.40 | 29.70 | 33.00 |
| 2L hiking bladder | 4.40 | |||||||||
| 3L hiking bladder | 6.60 | |||||||||
| 4L hiking bladder | 8.80 |
How Much Water Do You Need For Hiking?
And of course the next natural question here would be how much water do you really need when hiking? Several factors come into play here:
- hiker’s weight
- hiker’s age
- hiker’s daily energy intake (i.e. how many calories eaten per day)
- hiker’s sweat rate during hiking activity
- hours spent on the trail
- ambient temperature which affects sweat rate
- hiker’s exertion on the trail which affects sweat rate
Let’s break this question down into two parts:
What is a Person’s Normal Daily Fluid Requirements Outside of Hiking Related Sweating?
For a normal healthy adult we can take an average of a few methods.
The first is just the vanilla Holliday-Segar Method. This method assumes that a person’s fluid requirements are augmented due to heightened energy requirements from being ill in a hospital. But we could use that as a proxy for an active person, who also has heightened energy requirements. After all hikers are kind of active right?
For an adult:
1,500mL + 20mL(W – 20kg) = daily fluid requirement in mL for people at or under 50 years old; where W = weight in kg
1,500mL + 15mL(W – 20kg) = daily fluid requirement in mL for people over 50 years old; where W = weight in kg
1kg = 2.2lbs
30mL = roughly 1 US fluid ounce
The second method is just based on daily energy intake, and again, a hiker is going to have a higher energy requirement on their hiking day(s).
For an adult:
For every calorie eaten for the day, the hiker needs 1mL of fluid or 0.0338 US fluid ounces
Use my Total Daily Energy Needs for Hiking Calculator to get a rough estimate of you daily energy needs when your hiking, based on trail conditions.
One more method is just following this simple nomogram:
| Age in Years | Fluid requirement |
|---|---|
| >65 | 25mL/kg |
| 55-65 | 30mL/kg |
| 25-55 | 35mL/kg |
| 15-30 | 40mL/kg |
How Much Fluid Does the Act of Hiking Take (aka, What is a Hiker’s Sweat Rate)?
Beyond you base daily fluid requirement, your going to lose extra fluid through sweating, based on ambient temperature, how acclimated you are to the ambient temperature, how tough the trail is, and your personal sweat rate under those conditions. Because this is so variable from person to person – some people sweat 0.5L per hour during exercise, some sweat 2.5L – there’s no good way to estimate how much fluid you’re going to need when hiking. The only way to calculate your sweat rate is to personally measure it on hiking trial runs (weigh yourself before and after a sweaty hike, then take into account urine loss and fluid intake on the trail). I have a lengthy article on how to do that, called ‘Sweat, Mineral, and Micronutrient Losses Related to Hiking in Higher Temperatures‘ if you want to know exactly how to calculate your sweat rate.
Once you know your hiking sweat rate, then just multiply it by the number of hours you plan on hiking for the day and you can find how many liters of fluid are needed due to sweat loss.
Putting it All Together
To get a estimate of your total daily fluid needs and how much water per day you’ll need on a hiking day, just add your baseline needs to your sweat loss needs; that would be your daily estimated fluid needs. 20% of your daily needs are met through food intake, so keep that in mind if packing perfectly hydrated food (non-backpacking dehydrated food), or just eating at home or at a restaurant (day hiking).
Also keep in mind if you become dehydrated and your core temperature starts to rise due to it, then you’re going to need an extra 100-150mL of fluid for every degree Celsius (1.8F degrees) your core temperature rises for the day. And at that point you’re in trouble , so stay hydrated on the trail to not let it happen.
Example
Let’s just use our 70kg, 5ft 9in, 30 year old male, hiking 2 hours up a moderate sloping hill, and 2 hours down that same hill on a day hike. Our male is also active in his daily living activities (cleans his house, shops, and cooks the same day of the hike). This entails 3,600kcals of energy are needed for the day. He’s measured his sweat rate for this particular hike and ambient temperature and finds he loses 500mL per hour on average on the hike (more on the way up, less on the way back).
Calculation of Daily Fluid Requirements for Example Hiker
Holliday-Segar method = 2,500mL baseline
Energy intake method = 3,600mL baseline
Age based method = 2,800mL baseline
Average baseline = 3,000mL
Sweat related loss = 4 times 500mL = 2,000mL
Total daily fluid needs = 3000 + 2000 = 5000mL or 5L
Discussion
So basically he needs 5 liters of fluid for the entire day (plus enough sodium, potassium and chloride to avoid hypervolemic hyponatremia from taking in all that fluid). 1L will come through food intake, and he’ll need 4L of water to drink. So likely he’ll need to slowly take in 1L between when he wakes up and when he’s about to hike to make sure he’s hydrated (500mL a few hours before and 500mL 30 minutes before hitting the trail), then take in say 1.5L on the trail along with some salty foods or oral rehydration solution powder, then another 1.5L the rest of the day after the hike.
Now if he packed into a campsite the night before, on an easy 1 mile hike from the car, and is relying on dehydrated food, some Cliff bars, pouches of tuna, and beef/deer jerky, the day of his hike, then he might want to pack more than 5L of water for the day just to balance out all that sodium (250kcals of jerky may have 1.2g of sodium; 3 backpacking meals may have 3.6g of sodium; and he may only lose 2g of sodium in sweat for the day, leaving him with at least 2.8g intake, probably more from the other foods).
So he might want to pack a 4L bladder of water with a couple 1L bottles for the trail, or a grueling 13 pounds of water. 1.5L of that will go to redydrating the backpack food. Or he may want to just hike and chill for the day, dropping his energy and fluid needs by a few hundred milliliters. Or go in the off season when it’s not hot, or walk slower for less exertion.
Okay that’s it for now, happy hiking folks…
Further Reading
This article is part of my Hiking Nutrition Series where I talk about anything from day hiking energy needs to thru-hiking malnutrition. Check it out!