How Much Water Should You Carry on a Hike?

Water is, quite honestly, the most important thing in your bag on a hike. You can muddle through a surprising amount of kit choices, but you can’t magic more water into existence once you’re hot, thirsty and still a long way from the car.

My rule of thumb for a UK day hike is to start with at least 2 litres. That’s before I’ve looked at the forecast, the route or whether there’s a chance to refill. It might feel like a lot when you pick your backpack up at home, but it feels a lot less annoying when the sun comes out, the route takes longer than expected, or the water source you had pinned on the map turns out not to be one you’d want to drink from.

Start with 2 litres, then add what the day needs

There isn’t one number that works for every person or every route. A short winter walk on familiar ground is a very different day to six hours on an exposed ridge in July. You’ll need more if it is hot, if you know you sweat a lot, if you’re carrying a heavier pack, or if the route is long, hilly or remote.

For a beginner, I would always recommend you carry too much, rathan set off hoping a small bottle will do. As you then do more hikes, you’ll soon get a feel for what you personally drink on different kinds of days, which is useful information to take into your next plan.

The half-litre-an-hour rule is only a starting point

You will often see people online say you need half a litre of water for every hour you are walking. I don’t think it is a bad way to sense-check your plan, but it is not a rule you need to follow blindly.

Some days you’ll drink far less than that. On other days, half a litre an hour will not feel like enough. The heat, humidity, wind, how hard you are working, what you have eaten and your own body all make a difference. You also do not want to be stood at the trailhead trying to calculate your entire day down to the millilitre.

When you’re trying to work out how much to take, I would always start by asking yourself a series of questions: How long could this actually take me? Is there much shade? Is it exposed? Am I going somewhere with a reliable place to refill? What happens if I take a wrong turn or have to slow down? If the answers leave you unsure, take more water or choose a different route.

Carry it in a way you will actually use

It might sound silly, but once you’ve decided how much to take, deciding how to carry it can be just as much of a question, leaving you to venture down the water bottle v. water bladder rabbit hole. 

Bottles can be great for knowing exactly how much you have left. They’re are easy to fill, easy to clean and if you drop one or it leaks, you have not lost all of your water in one go. However, the downside is you’re less likely to drink as you go purely because you have to stop to dig it out of your bag any time you feel thirsty. 

Water bladders are great if you’re walking for a long time. Having the hose there makes it much easier to take little drinks regularly, rather than waiting until you stop. On the downside it is harder to see how much you have left, and they need a bit more care when it comes to cleaning and drying them properly.

Neither option is perfect. Some people like a bladder with one separate bottle as a backup. Some people prefer two big bottles. The best system is the one you will keep filled, carry comfortably and actually drink from.

Filters and purification are useful, but they are not a magic tap

A filter or purification method can make a massive difference once you are carrying more water than is comfortable or going on a multi-day hike. It means you can top up from a suitable source rather than trying to carry every litre you will need from the start.

They are not all the same thing though. A filter physically removes particles and, depending on the filter, certain microorganisms. Chemical treatments and UV purifiers work differently, and they each have their own instructions, treatment times and limitations. None of them makes water that is obviously polluted, oily, stagnant or contaminated with chemicals safe to drink.

You also need to think about the source itself. Just because you can see water on a map does not mean it will be running, easy to reach or suitable to use on the day. I would never plan a hike around a water source without carrying enough to get by if that plan does not work out.

For a normal day hike in the UK, I still carry the water I expect to need. A filter is a useful backup, particularly on long days, remote routes and multi-day trips. It is not a direct replacement for doing your water planning in the first place.

Make water the first thing you pack

Before you start filling your bag with all the nice-to-have bits of kit, sort out your water first. Fill it at home, check how much you have got and make a decision about whether you need more for the route you are planning on doing before you’ve made it out of the front door.

And don’t forget, you can always pour unused water away when you get back to the car. What you can’t do much about is being two hours from the end of a hike with an empty bottle and no good option to refill. Start with 2 litres, add more when the day calls for it, and treat your water plan as seriously as you treat the route itself.

If you’re working out water, timings and what needs to go in your bag, my free Hiking Planning Bundle includes a fillable route planner and a kit decision guide to help you put the plan together.