Water Carry Calculator

Why water carry needs a plan

Water is the heaviest thing most hikers carry, at about a kilogram per litre. Carry too little and a dry stretch becomes dangerous. Carry too much and you haul extra weight for hours. This calculator gives you a reasoned middle ground for each stretch between reliable sources.

It needs four inputs:

• Distance to the next water source you trust.
• Pace in km per hour, including the effect of climbing.
• Drinking rate in litres per hour.
• Safety reserve in litres.

It works out time to water (distance ÷ pace), then water to carry (time × drinking rate + reserve). Because a litre weighs about a kilogram, the weight figure matches the volume.

Worked example

A 12 km stretch at 3.5 km/h takes about 3.4 hours. At 0.6 L per hour plus a 0.5 L reserve, carry 2.6 L, which adds about 2.6 kg to your pack.

The same distance needs more than three times as much water in the hot, slow scenario. That's why you should plan each stretch for its actual conditions, not by distance alone.

Choosing a realistic pace

Map pace and real pace aren't the same thing. A common rule of thumb, often credited to Naismith, adds about an hour for every 600 m of ascent on top of walking time on the flat. If your stretch climbs a lot, lower your pace in the calculator to match.

Finding your drinking rate

Your own rate is better than any table. On a few training hikes, note how much you start with, how much you finish with and how long you were moving. Do this in different temperatures. You'll soon have a personal range. The calculator then turns that range into a carry plan.

Water and food planning

Some foods need water, like dehydrated dinners and oatmeal, and some don't. On a dry stretch, include cooking water in your carry, or switch to no-cook foods for that section. Our guide to no-cook backpacking meals has ideas. The hiking calorie estimator uses the same moving-time idea for energy.

Important safety notes

• Treat this as a planning estimate. Weather, injury or a dry source can change everything.
• Check current water source reports where they exist, and have a backup plan.
• Treat or filter natural water as local guidance recommends.
• Signs of heat illness and dehydration need prompt attention. Learn them from a reputable first-aid source before hiking in heat.

This tool doesn't replace local knowledge, ranger advice or good judgement.

How to use the calculator, step by step

1. Mark your reliable water sources on the map or in your route notes. Note which ones are seasonal or uncertain.
2. Measure the distance between them. Use the distance to the next source you trust, not the next blue line on the map.
3. Estimate your pace for that stretch, slowing it for climbs, rough ground or heat.
4. Pick a drinking rate from your own experience, or start from the guide table below and adjust.
5. Choose a reserve based on how sure you are about the next source and how bad a delay would be.
6. Read the result, then add any cooking or camp water if you'll stop before reaching the source.

Drinking rate guide

These are starting points only. Personal rates vary widely with body size, fitness, clothing and acclimatisation, and you should replace them with your own numbers as soon as you can.

Public health and outdoor organisations often advise drinking regularly and adjusting for heat and effort, rather than following a single fixed figure.

Choosing a reserve

The reserve isn't for drinking on schedule. It's for the unexpected: a wrong turn, an injured partner, a source that's dry or contaminated.

Worked example: a two-day route with a dry camp

A made-up route, with three stretches:

The middle stretch is the big carry, at 4.2 L. The last stretch ends at a dry camp, so add camp water to it: perhaps 0.5 L for dinner, 0.5 L for drinking in the evening and 0.5 L for breakfast. That makes the carry from the lake about 3.4 L, enough to reach the next source the following morning, if it's close. For a longer morning stretch, calculate that one too and carry its water from the lake as well.

Dry camps

A dry camp means sleeping away from water. It can be a great choice for views, shelter or quiet, but it means carrying water for:

• Dinner and breakfast, especially if you cook. Dehydrated meals often need 300 to 500 ml each; check the packet.
• Evening and overnight drinking.
• The morning walk to the next source.
• Cleaning pots and teeth, usually only a little.

Planning food with low water needs can cut the carry. Cold-soak meals still need water, but no-cook foods like wraps, cheese and nuts need almost none.

Water weight and your pack

Water changes your pack weight more than anything else during the day. Carrying 4 L adds about 4 kg at the start of a stretch, which falls steadily as you drink. If you're using the hiking calorie estimator, you can use an average pack weight for a long carry, such as the start weight minus half the water.

Heat and timing

In hot weather, the most effective change is often when you walk, not how much water you carry. Starting at dawn, resting in shade at midday and walking again in the evening can cut your drinking rate a lot. If the calculator shows a carry you can't manage safely, change the plan: start earlier, choose a different route, add a water cache where allowed, or pick a cooler season.

Measuring your own drinking rate

Here's a simple test you can do on any training hike:

1. Fill your bottles and note the total, for example 2.0 L.
2. Hike as normal and note your moving time, for example 3 hours.
3. At the end, measure what's left, for example 0.5 L.
4. Divide what you drank by moving time: 1.5 L ÷ 3 h = 0.5 L per hour.

Write down the temperature, sun, terrain and how you felt. After five or six hikes you'll have a personal table that's far more useful than any general guide. Remember that feeling fine at the end matters: if you finished thirsty or with a headache, your real need was probably higher than what you drank.

Group water planning

In a group, calculate for each person, since drinking rates differ. Then:

• Share the carry fairly by body size and pack weight, not equally by default.
• Keep a group reserve with the person most likely to stay with the slowest walker.
• Agree on a turn-back point if a source on the plan turns out to be dry.
• Treat water in batches at each source so everyone leaves with full bottles.

Water treatment

Water from natural sources can carry germs even when it looks clear. Common options are filters, chemical treatments such as chlorine dioxide, UV devices and boiling. Each has its own strengths, limits and contact times, so follow the product instructions and local health guidance. Boiling uses fuel, so include that in your stove plans if it's your main method.

Reading water reports

On popular long trails, hikers and land managers often share water source reports. They're very useful, but they're also snapshots. A spring reported as flowing two weeks ago can be dry after a heatwave. When in doubt, plan to carry to the next source as well, and treat the reported one as a bonus.

Glossary

• Reliable source: a source you have good reason to expect will have water when you arrive.
• Dry stretch: a section with no reliable water.
• Dry camp: a campsite without water.
• Reserve: extra water carried for delays and surprises, not for normal drinking.
• Water cache: water left ahead of time, only where it's allowed and you'll collect the containers.

Water-friendly food choices

Food and water are linked. Dry foods like crackers and nut butter can make you thirstier, while some foods carry water with them. On a long dry stretch:

If a stretch is very long, moving the cooked dinner to a day with plenty of water and eating no-cook food on the dry day can save a litre or more of carry.

Common mistakes

1. Trusting every source on the map. Seasonal streams and old springs can be dry.
2. Using flat pace for a climbing stretch.
3. Forgetting cooking water for a dry camp.
4. Drinking the reserve early and then counting on it later.
5. Copying someone else's drinking rate. Measure your own.
6. Ignoring electrolytes. On long, hot days, salty foods or electrolyte drinks help replace what sweat removes.

Related tools and guides

• Hiking calorie estimator: energy for the same stretch.
• Trail meal planner: plan meals around water availability.
• No-cook backpacking meals: food for dry stretches.

Splitting water across containers

Once you know the total, think about how to carry it. Several smaller bottles let you track how much you've drunk and spread the weight. A collapsible bladder is light when empty and useful for big carries. Keep at least one bottle easy to reach so you drink steadily instead of in big gulps at breaks. Put the heaviest water close to your back and centred in the pack, which keeps the load stable. Mark bottles, or keep the reserve in a separate container, so you always know how much of your reserve is left. Before leaving each source, check that every container is full and tightly closed.