Backpacking Water Need Calculator

1. Set your drinking rate in litres per hour for the conditions.
2. Enter the hours until you can next refill.
3. Add a safety reserve for a dry source or a delay.
4. Read the water to carry and its weight.

Backpacking water need is how much water to carry between reliable sources. Water is heavy, at about a kilogram per litre, so carrying too much slows you down, while carrying too little is genuinely dangerous. The aim is to leave each source with just enough to reach the next, plus a sensible reserve.

Your need depends on how hard you are working, the heat, the altitude and the gap between water points. Planning it in advance is a core skill on dry routes where the next spring might be hours away.

1. Estimate your drinking rate in litres per hour for the conditions.
2. Multiply by the hours until the next source for your drinking need.
3. Add a reserve in case the source is dry or you are slower than planned.
4. Remember each litre adds about a kilogram to your pack.

A rate of half a litre per hour suits mild conditions and steady walking; hot weather, hard climbs and altitude can push it to a litre an hour or more.

The next reliable stream is 5 hours away and conditions are mild, so you plan on half a litre per hour. That is 2.5 litres to drink. Adding a half litre reserve gives 3 litres to carry, weighing about 3 kilograms. On a hot day at three quarters of a litre per hour, the same 5 hour gap would need 3.75 litres plus reserve, close to 4.5 kilograms of water alone.

Heat and Sun

Hot, exposed days sharply raise sweat loss and your drinking rate.

Effort and Climb

Hard climbing with a heavy pack burns through water faster than gentle walking.

Altitude

Higher altitude increases breathing and fluid loss, so you need more than at sea level.

Source Spacing

The longer the gap between reliable water, the more you must carry and the heavier your pack.

Typical hiking drinking rates for planning; adjust to how you actually feel.

These are planning figures, not limits. Drink to thirst, watch for dark urine, and never ration below what your body needs.

Planning a Dry Route

Work out how much to carry across long gaps between springs or taps.

Balancing Weight

See the weight cost of water so you carry enough without overloading.

Hot-Weather Days

Raise your rate and reserve for heat, sun and hard effort.

1. Underestimating Heat

Hot days can double your drinking rate; plan for the conditions, not a mild average.

2. No Reserve

Sources dry up and plans slip; always carry a reserve beyond your drinking need.

3. Ignoring the Weight

Water is heavy, so carrying far more than you need tires you unnecessarily.

4. Trusting Unreliable Sources

If a source may be dry or dirty, plan to carry through to a reliable one and treat what you collect.

The maths is exact for the rate, time and reserve you enter. Your real need varies with heat, effort and your own body, so treat it as a planning guide.

Multiply your drinking rate by the hours to the next source, then add a reserve. At half a litre an hour for 5 hours plus a 0.5 litre reserve, carry 3 litres.

About 0.5 litres per hour in mild conditions, rising to 0.75 to 1 litre or more in heat, at altitude or on hard climbs.

About 1 kilogram per litre, so 3 litres weighs roughly 3 kilograms. Water is often the heaviest single item on dry routes.

Sources can be dry, dirty or further than expected, and you may be slower than planned. A reserve covers those risks.

Yes, a lot. Hot, exposed days can double your drinking rate, so raise both the rate and the reserve.

Map the reliable sources, work out the hours between them, and calculate the carry for the longest gap, plus a reserve.

No. Carry enough for the gap; rationing below your need risks dehydration. Save weight elsewhere, not on water.

Yes. Higher altitude increases breathing and fluid loss, so you need more water than at sea level for the same effort.

No. The calculator runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Hiking and hydration (Wikipedia).
• Water and the human body (Wikipedia).
• Dehydration (Wikipedia).