How much water?

Drink lots of water before you start, like 1 liter

Carry 1/2 liter

You'll be a little dehydrated at the end

Maybe you want a little more than that just for safety, especially if there is unlikely to be anyone else walking by

This is one of those things that will vary for each individual. Some will be fine with 1 liter and others need more than 2. Over time you will learn what works for you.

Yeah, 1/2 liter is on the low end, most people more like what Nick said

But why carry more than you need?

For that I would drink a liter in the morning and carry two liters if there is no water available. Everybody is different. Some would require 1 liter and others 3+ liters.

Point Reyes is my neck of the woods. I'd suggest 1.5 to 2 liters, plus drink up before you start your hike. Also, the water at the campgrounds sometimes has a little old rusty pipe flavor, so flavored drink mixes can be a welcome addition to your menu.

I calculate a liter every three miles but with the temperatures you're describing I'd probably be ok with less. If it was me, I'd tank up at the trail head and carry two liters.

There are plenty of people who would be fine with a liter in that distance but if you're not sure then I wouldn't leave with less than two; (edit) this way you can chalk this up as a learning experience about what you can tolerate and add/subtract from that amount the next time you find yourself in this situation.

liter for 3mi at 70F? hehe i'd drowned. Last weekend I accidentally did around 18mi on 1 liter.. was only empty for 2.5mi though (that part hurt a bit though). did 11mi out the next day with 1 liter.

definitely a personal experience thing.

18 miles on one liter is pretty impressive. I'd die. Was this in the Whites? Most of the hikes I go on in the Cascades you're hitting a water source every 1/4 mile so in many cases carrying 20oz would be overkill.

I live in the desert side of Washington. I hiked a local mountain this morning. First mile was just 800' in 85* and I killed a liter no problem before the top. Same grade in the Cascades in 70* weather and I doubt I'd drink half of that.

Different strokes for different folks. Per the Army, drinking water cures everything from scurvy to shin splints so old habits die hard I suppose.

It was in the Whites.. my TR is in the TR section.
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Starting at 6am has it's advantages too. not too hot out. I crossed a half dozen stream/rivers when I didn't need it and then it was dry from the hut until shelter.

I meant to refill my bottle at one of the huts when I went by but got distracted talking to an AT NOBO and forgot. I got to the shelter, drank 1/2 liter immediately, hiked another 1.5ish mile without my pack out and back to another peak then had the rest of the liter with dinner.

I'm also a small guy 5'7 125, don't sweat a ton, and between rock climbing and cycling i'm used to sometimes being without a lot of water. I never felt too wonky.. at that point it was more annoying being thirsty than dehydration. ie. today i rode 42mi with 24oz of NUUN.

I mentioned above that I hiked a local mountain on Saturday in 85* weather (daytime highs reached 100.) I live in the desert so the air is very dry. We killed a liter each before reaching the top which is about a one mile hike.

Sunday I hiked the same mountain and incorporated a six mile loop. We started at 6am and the temperatures were 64* with a breeze. We both drank a liter each in the six miles and would have been fine with less.

Just wanted to show what a difference it can make when you change one variable.

As I mentioned before, when I plan a trip I try to determine if I will hit a water source at least once every three miles. If so, then I'll carry 20-32oz of water depending on the conditions. If not then I adjust accordingly.

I still stand by my previous recommendation. If you are really not sure how much water you will need, I'd tank up at the trailhead; drink until your urine is clear. Carry a couple liters on your hike and see how much you have left at the end and use that as a baseline for future trips. Add more when hotter, more elevation gains, less when not, etc.

Temperature means everything. Anything near 80+ degrees and I plan for more water or cutting the miles down.

I JUST GOT BACK from a 3-day at Point Reyes!! My partner was a water hound and insisted we carry 2 liters each. It was way too much. I could have made do with 1 liter, and I think 1.5 liter would give a nice buffer.

The water in the camps, BTW, is potable but not tasty. (Was told it was stored in campsite tanks.) Quite a bit of chlorine taste. Bring your drink powders to disguise the taste.

My strategy is to carry more than I need and drink most of it early in the hike.