Emigrant Wilderness, August 2025
I had hiked 18 miles with a 50-pound backpack. Then, I cached 40 pounds of food and started a little overnight bushwhack loop to visit some new-to-me alpine basins.
It was sunny, hot, and dry.
And I was tired of carrying pack weight, so I looked at the map and poured out my water. I’d tank up at water sources.
An hour later, I reach the first creek. It was dry.
After another hour, the pond that was on the map turned out to be a putrid cesspool of mosquitoes, slime, and a rotting deer carcass. I skipped that and kept moving.
Finally, after three and a half hours and five miles of bushwhacking since I poured out my water, I heard the glorious sound of running water while sidehilling up a steep canyon. I made a beeline to the bottom, dropping 300 feet of elevation just for the chance at some cool liquid refreshment:
By the time I arrived at the creek, my heart was racing, my legs were shaking, and my nerves were on edge.
I drank two liters at the creek and packed another two for the 3-hour climb out of the canyon, over a pass, and into the drainage where I was aiming to camp.
This experience had me revising The Water Question we often ask as practitioners of ultralight:
Should I carry water, or tank up at water sources?
That decision comes down to how fast dehydration changes your physiology – and the math isn’t in your favor if you skip drinking for too long.
The Numbers
A 160-pound hiker carries about 44 liters of body water. Losing 1% of body mass as water (i.e., 0.73 liters, about 25 ounces) is the first threshold where performance starts to slip.
How long does it take to lose that much without drinking?
- Cool/easy pace (~0.3 L/h loss): ~2.5 hours
- Moderate/warm (~0.6 L/h loss): ~1.2 hours
- Hot/hard (~1.0 L/h loss): ~45 minutes
Those numbers shorten if you’re smaller, heavier, or sweating more than average.
What Happens at Each Stage
1% loss (~0.7 L): Thirst kicks in. Mental sharpness dips – you may not notice (that’s part of it), but pay attention to your decisions here.
2% loss (~1.5 L): Endurance drops 5–10%. Climbs feel harder, heart rate climbs, heat feels oppressive.
3% loss (~2.2 L): Now you’re degraded – dizziness, slow reaction time, poor judgment.
5% loss (~3.6 L): Crisis. Nausea, confusion, high risk of heat exhaustion or worse.
The Lessons
Dehydration arrives fast. In warm conditions, you can cross the 1% line in under an hour.
Matching intake to loss (roughly 0.4–1.0 L/h, scaled to conditions) keeps you stable. It does pay to carry water if dehydration is a risk and water sources are scarce.
Cognitive decline affects navigation and safety as much as muscle fatigue does – so don’t forget that dehydration isn’t just a physical problem. The body and mind are intertwined and feed off each other. If one starts to fail, the other isn’t too far behind.
The Takeaway
When you weigh the choice between carrying water and tanking up at sources, the physiology leans one way: steady hydration keeps you sharper, safer, and more efficient. The ounces in your bottle may feel heavy, but the cost of skipping them compounds quickly.
So, should you carry water, or tank up at water sources? At least carry enough to keep the needle below 1%.
Discussion
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Skipping water for lighter pack weight can backfire. Learn how quickly dehydration sets in, what happens at 1–5% body water loss, and whether it’s safer to carry water or tank up at sources.
I had quite an experience last year when I started a new blood pressure medication that was also a diuretic. Considerable adventures ensued.
I’ve learned that I need both water and electrolytes when I am hiking in the Sierra, and in quantities: at last two liters of water per day, plus a liter of electrolytes. Others may have different needs.
And yeah, I did get that prescription adjusted. Much better now.
This seems to be a common scenario. I changed doctors. I’ve seen a couple different doctors since. I’ve been off of diuretics for over ten years. At least in my case, I didn’t need them.
Yeah, just change doctors until they say what you want.
That’s pretty funny
LOL. I didn’t change doctors, by the way. I just told him what happened, and he agreed that there were other ways to achieve lower blood pressure. I still take the initial medication, but without the secondary one which was the diuretic.
Well I was a bit snarky, but also straight up. In fact, a close friend switched cardiologists when one told him some 20+ years ago to quit mountain biking. That is like saying, quit living. So he found a new one who could lay it out straight and tell him the honest risks; my friend found they were risks worth taking and has biked ever since!
But back to water – I always have at least 1 liter with me. I’d rather carry it than not have it and want it. It’s only 2 pounds, quickly lightened.
😁Funny, however it’s true. If I don’t agree with a doctor, I’ll go elsewhere. Sometimes they’re right, sometimes they’re wrong.
I’ll cool myself down at a water source. I hydrate, but I don’t normally tank up. I don’t want a full belly, unless maybe I’ve lost my container.
okay, I take that back, even though it’s pretty funny, it’s also snarky. It’s not critical of anyone in particular, like Paul, but it does happen that sometimes people will seek out a doctor that says what they want even if it’s bad advice.
For years I took occasionally increasing does of lisinopril that I thought was lowering my BP, but actually I was mistaken because I wasn’t measuring my BP carefully enough. My BP stayed at 140/90.
Then, a doc told me to measure my BP 10 times over several days at different times of the day and average it. Using that I figured out that just lisinopril wasn’t doing anything.
Then another doc prescribed the diuretic in addition. That lowered my BP to 120/80. When I took just the diuretic, it went back up to 140/90 – both medicines work together to lower my BP. My doc said that would likely happen.
If you can get your BP to 120/80 there’s a little less risk of getting a heart attack or stroke. It’s not something you can tell from what you experience. I felt fine at 140/90. You have to trust studies and doctors.
Or, you can ignore all this and have a BP of 140/90 and have a little higher risk. Likely you can get away with it without problem.
Great, concise article!
It’s important to remember that many water sources are seasonal and just being on a map doesn’t guarantee water.
appreciate the article.
First the reminded that water sources on map aren’t necessarily reliable. I still haven’t learned this lesson… unless I know from others trip reports that a source is gone/poor I have a tendency to expect it to be good even though experience should warn me that this is an unfounded assumption. Doh!
I ran experiments measuring my rate of lose (160lb male) and found my numbers are pretty close to Ryan’s with one addition level. When it’s >85F and I am >=7 METs I lose around 3L! of water in an hour.
super useful to know 2% is around when heart is racing. Certainly have experienced that. Also to testify to the need of electrolytes. A few years ago, on the same trip that my my heart rate would normally be 120-140bpm and it was pegged to 160bpm (going up after maybe 10 steps) I had almost every muscle in my body cramp. Took around 10 minutes to move enough to retrieve electrolyte powder and add it to water. After drinking it continued to cramp with just about any movement for between 15-30 minutes and then, the cramping went away.
The one question not directly answered is can you get ahead of dehydration by cameling up. That is drink more than you have lost now, so when you lose more later, you still have buffer.
if you drink too much you just immediately pee it out. Plus, that includes a bunch of sodium making your electrolytes imbalanced.
I haven’t cramped during the day, just at night
Once I forgot to drink or eat for quite a few hours. It was raining and I didn’t want to stop and get my stuff out.
Then I hit a wall – my feet became filled with lead, I could barely move.
I got to a shelter, ate and drank, 15-30 minutes later was fine. I don’t know if it was water or food or both.
Now, I make sure and eat and drink occasionally even if I don’t feel the need.
many times I have seen a river or lake on a map and thought there was water. When I got there it was dry. Or mucky.
now-a-days, I’m more likely to go somewhere I’ve been before so I know where the reliable water is.
I deserved that one^^^^no harm. A little humor is good.
Accessibility can change yearly. I went on a river trail a few weeks ago that went up the side of a hill. I could see the river.
I also used to subscribe to the camel up practice. Not any longer-almost all of my hikes where my electrolytes were way off involved a pre-hike(or during if we found a source) chug fest of water. 2L or so with 15 min. Even when adding electrolyte packets I still suffered, had a sloshing belly of water and cramped up bad during the hike.
I don’t do that anymore. Many can get away with it but I’m not sure it really helps in any measurable way.
Also on a low dose diuretic bp medicine for years,
One key, as your dispatch noted, is the reliability and condition of your planned water sources. If there’s any doubt at all or if you don’t have a recent report of ample water, then carry what you need.
Dan
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